Nasdaq: CBIO CATALYST BIOSCIENCES Corporate Overview 17 September 2020 CatalystBiosciences.com Catalyst Biosciences Forward looking statements This presentation includes forward-looking statements that involve substantia

Nasdaq: CBIO CATALYST BIOSCIENCES Corporate Overview 17 September 2020 CatalystBiosciences.com Catalyst Biosciences

Forward looking statements This presentation includes forward-looking statements that involve substantial risks and uncertainties All

statements included in this presentation, other than statement of historical facts, are forward-looking statements. Forward-looking statements include statements about the potential benefits of products based on Catalyst s engineered protease

platform; potential markets for and advantages of MarzAA and DalcA; plans in Q4 2020 to enroll a pivotal Phase 3 registration study of MarzAA , initiate a Phase 1/2 trial in FVII Deficiency, Glanzmann Thrombasthenia, and patients treated with

Hemlibra and initiate a pivotal non-human primate study of CB 2679d-GT; the potential for MarzAA and DalcA to effectively and therapeutically treat hemophilia

subcutaneously; potential markets for our anticomplement and gene therapy programs; potential payments from Biogen; plans to declare a development candidates in our systemic complement program in Q4 2020; the superiority of CB 2679d-GT over other gene therapy candidates; and the Company s collaboration with Biogen for the development and commercialization of pegylated CB 2782 for the potential treatment of geographic

atrophy-associated dry age-related macular degeneration (AMD). Actual results or events could differ materially from the plans, intentions, expectations and projections disclosed in the forward-looking

statements. Various important factors could cause actual results or events to differ materially, including, but not limited to, the risk that trials and studies may be delayed as a result of the novel coronavirus

(COVID-19) outbreak and other factors, that trials may not have satisfactory outcomes, that additional human trials will not replicate the results from earlier trials, that potential adverse effects may arise

from the testing or use of DalcA or MarzAA, including the generation of neutralizing antibodies, which has been observed in patients treated with DalcA, the risk that costs required to develop or manufacture the Company s products will be

higher than anticipated, including as a result of delays in development and manufacturing resulting from COVID-19 and other factors, the risk that Biogen will terminate Catalyst s agreement, competition

and other risks described in the Risk Factors section of the Company s quarterly report filed with the Securities and Exchange Commission on August 6, 2020, and in other filings with the Securities and Exchange Commission. The

Company does not assume any obligation to update any forward-looking statements, except as required by law. Catalyst Biosciences

Catalyst Biosciences Protease medicines Protease engineering platform Late-stage asset SQ Marzeptacog alfa (activated) MarzAA

(FVIIa) Phase 3 in 2020 Hemophilia SQ MarzAA (FVIIa) SQ Dalcinonacog alfa DalcA (FIX) Factor IX Gene Therapy Factor Xa Complement IVT Anti-C3 Dry AMD CB 2782-PEG

SQ Systemic Complement Inhibitors Catalyst Biosciences

Harnessing the catalytic power of proteases One protease molecule activates or inactivates 1000s of target molecules Therapeutic

Protease Target Protein Specific Cleavage Site An adaptable protease platform Functionally enhanced natural proteases (FVIIa, FIX) Engineered novel protein degraders (Anti-C3) Extended half-life variants

Increased potency Proven efficacy of clinical stage assets Advantages Quick & simple SQ dosing for systemic use Less frequent intravitreal dosing in ophthalmology Low vector dose gene therapy constructs Ideal for high concentration drug

targets or controlling amplification cascades Catalyst Biosciences

Pipeline Hemostasis SQ Marzeptacog alfa MarzAA (rFVIIa) Hem A or B w/ Inh ToB FVIID/Glanzmann/Hemlibra

ToB SQ Dalcinonacog alfa DalcA Hem B (rFIX) FIX-Gene Therapy Hem B (CB 2679d-GT) Complement IVT CB 2782-PEG Anti-C3 protease for Dry AMD SQ systemic complement inhibitors CB DC Catalyst Biosciences R PC P1/2 P2 P3

Investment highlights Novel subcutaneous factors with orphan drug designation, MarzAA & DalcA P2 efficacy in prophylaxis

studies complete Multibillion-dollar market opportunities Strong balance sheet, $117.4 M cash Q2 Anti-C3 Dry AMD with Biogen SQ systemic complement regulator research program Experienced team 177

worldwide patents CBIO retains full ownership of all compounds Catalyst Biosciences

Addressing unmet needs in rare bleeding disorders SQ treatment of episodic bleeding and prophylaxis $4B+ market Hemophilia A w/

Inhibitors MarzAA & DalcA Hemophilia B Prophylaxis Hemophilia B w/ Inhibitors Hemophilia A Factor VII Deficiency Glanzmann Thrombasthenia Acquired Hemophilia Catalyst Biosciences

Marzeptacog alfa (activated): MarzAA rFVIIa Addresses a clear unmet need in hemophilia & other bleeding disorders P129A T128N

M298Q Q286R Increased procoagulant activity Four amino acid substitutions + Multiple advantages over NovoSeven RT + 9-fold higher activity vs NovoSeven RT + Potency allows for SQ dosing Only SQ bypass agent

for on demand treatment + Small volume SQ administration + Improved bioavailability + Prolonged half-life Orphan Drug Designation in US and EU Catalyst Biosciences

MarzAA Phase 2 demonstrates efficacy with daily prophylaxis Annualized bleed rate n = 9 Proportion of days with bleeding n = 9 19.8

12.3% 1.6, p = 0.009 0.8%, p = 0.009 6 m pre-treatment On treatment 6 m pre-treatment On treatment Mahlangu et al. EAHAD

2020 + Greater than 90% reduction in all bleeding Median ABR = 0 + 7 of 9 subjects had no bleeding at final dose level + Safe & well tolerated, ~1% ISR (6/517 doses) & no ADA

Current bypass agents require multiple IVs over the course of hours Patients identify a need for an easy to administer treatment to stop

bleeds quickly NovoSeven 6 Hours + Patients reported needing an average of 6 hours and 3 injections of NovoSeven to resolve bleeds, with certain bleeds requiring up to or longer than 72 hours to resolve bleeding episodes1,2,3 Hours I have

trouble securing a vein for IV administration due to the fact that my veins are very scarred from years of IV injections. My veins are prone to collapse. Hemophilia Patient Wish we could do [treatment of a bleed] via something

outside of IV, we would love the convenience of a subcutaneous administration. Hemophilia Patient Source: 1NovoSeven PI Rev 7/2020; 2Adivo Associates market research; 3Catalyst Biosciences market research. Data on file Catalyst

SQ treatment of a bleed is a large commercial opportunity Global NovoSeven sales breakdown by indication (2019) $139M $63M $93M $578M

$1.22B $81M $263M Hem A Inh (47%) Other (22%) Glanzmann (7%) Hem B Inh (11%) FVII Def (5%) AHA (8%) SQ MarzAA has a superior profile Faster & easier to administer vs N7 dosed every 2 hours IV MarzAA half-life ~8x longer than N7 9-fold

higher activity vs N7 Potential to reduce rebleeding Stops bleeding in multiple preclinical models Can be combined with Hemlibra in vitro without increased thrombogenicity Potential for prophylaxis Ideal for pediatrics and patients with venous

access issues Source: Adivo Associates market research; Catalyst Biosciences market research. Data on file Catalyst Biosciences

MAA-102: PK MarzAA levels support SQ treatment of a bleed + Target of 24-120 ng/mL to treat a bleed is based on continuous infusion levels of NovoSeven for surgery + Target levels are rapidly achieved + 25% and 50% of Cmax at 1 and 2 hours, respectively + Dose-proportional increases

in Cmax and AUC + Target levels can be maintained for 18 hours with a single SQ dose of 60 g/kg + Multiple dosing cohorts completed , 60 g/kg every 3 hours; twice and thrice + No ADA Neuman et al. ISTH 2020

Catalyst Biosciences

Crimson 1 Phase 3 study: Treatment of episodic bleeding Hemophilia A or B with inhibitors N = 30 MarzAA SQ 60 g/kg 1-3 doses 5 bleeds per patient 130 per sequence bleeds N = 30 SOC IV 1-3 doses 5

bleeds per patient 130 per sequence bleeds SOC IV 1-3 doses 5 bleeds per patient 114 sequence bleeds per MarzAA SQ 60 g/kg

5 bleeds 1-3 doses per patient 114 per sequence bleeds Primary endpoint Non-inferior hemostatic efficacy: standard 4-point scale Secondary endpoints Time to bleed resolution; number of doses; rescue meds Safety Adverse events, anti-drug antibodies (ADA); thrombosis Statistics + SOC estimate

85% Excellent/good treatment of bleeds + Non-inferiority margin of 12% + 2.5% significance, one-sided + 90% power Catalyst Biosciences

MAA-202 Phase 1/2 study design FVII deficiency, Glanzmann thrombasthenia and HA on Hemlibra: N =

8 each Phase 1 PK MarzAA IV each cohort Single dose MarzAA SQ Single dose escalation Multiple dose Q3H Phase 2 ToB MarzAA SQ 1-3 doses FVIID 30 bleeds GT 30 bleeds HA 15 bleeds Phase 1 Primary endpoints: Pharmacokinetics Secondary endpoints: Pharmacodynamics Phase 2 ToB Primary endpoints: Hemostatic

efficacy at 24 hours Secondary endpoints: Effective hemostasis at successive timepoints; doses needed; rescue meds Safety: Adverse events and ADA Catalyst Biosciences

MarzAA clinical development plan for treatment of bleeds Large commercial opportunity across multiple rare bleeding disorders Initiate

P3 Crimson 1 study in Q4 2020 HA/HB with inhibitors Initiate P1/2 study MAA 202 in Q4 2020 FVII deficiency, Glanzmann thrombasthenia, Hemlibra breakthrough bleeds Data expected in 2021 & 2022 Catalyst Biosciences

Dalcinonacog alfa: novel FIX replacement for SQ delivery R318Y Resistance to T343R antithrombin R338E Increased FVIIIa

affinity & procoagulant activity Three amino acid substitutions + Increased catalytic activity + Higher affinity for FVIIIa + Resistance to antithrombin inhibition + 22-fold increased potency vs

BeneFIX Differentiated from marketed IV FIXs + Small volume SQ administration + Enhanced pharmacokinetics with prolonged half-life + Excellent extravascular distribution + Potential to maintain continuous protective levels Orphan drug designation in

US & EU Catalyst Biosciences

Dalcinonacog alfa Phase 2b SQ clinical trial Trial completed Endpoint achieved with steady state FIX activity levels >12% Initial 35

min post-IV DalcA IV DalcA SQ 50 IU/kg 100 IU/kg Daily SQ dosing to Day 28 DalcA SQ 100 IU/kg Wash-out Daily FIX activity levels measured for 5 days + Primary endpoint:

Steady state FIX activity level above 12% with daily dosing + Secondary endpoints: safety including weekly ADA testing, pharmacokinetics, pharmacodynamics, bleeding events + 6 severe Hemophilia B subjects dosed + Rare

propeptide mutation excluded + HLA profile associated with nAb risk was excluded Catalyst Biosciences

Dalcinonacog alfa Phase 2b SQ clinical trial Trial completed Endpoint achieved with steady state FIX activity levels >12% Initial 35

min post-IV DalcA IV DalcA SQ 50 IU/kg 100 IU/kg Daily SQ dosing to Day 28 DalcA SQ 100 IU/kg Wash-out Daily FIX activity levels measured for 5 days + Primary endpoint:

Steady state FIX activity level above 12% with daily dosing + Secondary endpoints: safety including weekly ADA testing, pharmacokinetics, pharmacodynamics, bleeding events + 6 severe Hemophilia B subjects dosed + Rare

propeptide mutation excluded + HLA profile associated with nAb risk was excluded Catalyst Biosciences DalcA P2b demonstrated proof of safety and efficacy Target levels >12% achieved with 100 IU/kg dosing for 28 days Factor IX Activity (%)

Days Wash Out Level Target + Dosed 6 severe HB subjects , Subject 102 withdrew on Day 7 + Steady state FIX levels up to 27% achieved after 14 days + No breakthrough bleeds + No neutralizing ADAs + Consistent PK profiles + Terminal

half-life is 2.5 5.1 days Catalyst Biosciences

Dalcinonacog alfa Potential to provide effective SQ prophylaxis for individuals with Hemophilia B Phase 2b trial complete Protective

therapeutic FIX activity levels achieved No bleeding events during treatment indicates effective prophylaxis No SAEs, systemic hypersensitivity, nAb Mild to moderate ISR primarily with initial injections transient & self-limiting

Long half-life potential for lower dose/reduced dosing frequency Catalyst Biosciences

Catalyst s CB 2679d gene therapy Limitations of 1st generation GTs create an opportunity AAV serotype - High vector doses

needed to achieve stable expression Preexisting neutralizing antibodies to the capsids limit efficacy & eligible patients Variable tissue tropism can limit effectiveness Durability + FIX transgenes encode the Padua high-activity

FIX variant Gene therapies have yet to demonstrate durable and clinically meaningful FIX expression 5 years post-infusion FIX activity has decreased over time Catalyst Biosciences

CB 2679d-GT for hemophilia B Engineered Capsid Novel Transgene Lower AAV Dose FIX AAV Study Dose

FIX Activity Transgene Capsid (vg/kg) (U/mL) Novel 10 CB 2679d-GT 8.0x10 20 Chimeric Padua TAK-748* 7.4x1011 20 Padua TAK-748*

7.4x1010 1 *Weiller et al. (2019) Blood Vol. 134, Supplement S1 P4633 License & sponsored research agreement CB 2679d-GT has a superior profile vs. Padua in preclinical studies + Stable high

activity levels with a vector dose reduced 10-fold in a mouse hemophilia B mode + 4 to 5-fold reduction in bleeding time when compared to the Padua transgene in mice +

Potential for an improved efficacy & safety Achieved high initial FIX levels in NHPs + Presented at World Federation of Hemophilia Virtual Summit 2020 (June 19, 2020) + Additional vector optimization & dose ranging studies ongoing

Wholly-owned & issued patents covering gene therapy Catalyst Biosciences

Targeting complement a pathway regulated by proteases Dysregulated complement activity is associated with a broad range of

disorders and a logical fit for our protease platform Antigen Classical antibody pathway complexes Lectin Pathogen pathway surfaces Activating Alternate

surfaces and pathway C3 tick-over CB 2782-PEG Targeting C3 blocks downstream complement Immune response inflammation Membrane attack complex (MAC) Autoimmune diseases Inflammatory

diseases Multiple rare diseases Catalyst Biosciences

CB 2782-PEG: Complement factor 3 (C3) cleaving protease Geographic atrophy in dry AMD can result

in blindness + Geographic atrophy is an advanced stage of dry age-related macular degeneration (dAMD) + Dry AMD affects ~1M people in the US and over 5M worldwide + Global market estimated at >$5B + C3 is

the only clinically (randomized P2) validated target for the treatment of dAMD + No currently approved therapy Sources: National Eye Institute. Facts About Age-Related Macular

Degeneration, Tufail 2015, The Eye Diseases Prevalence Research Group 2004, GlobalData Catalyst Biosciences

CB 2782-PEG long acting anti-C3 protease Best-in-class anti-C3 profile for dry AMD with dosing every 3 to 4 months Non-Human Primates C3

Concentration (nM) Time (days) CB 2782-PEG Concentration (nM) Human Modeling (nM) Concentration C3 Time (days) Predicted >90% elimination of C3 at 4 months Catalyst Biosciences

CB 2782-PEG long acting anti-C3 protease Best-in-class anti-C3 profile for dry AMD + Generated from Catalyst s proprietary protease engineering platform + Potent,

selective and long acting anti-C3 protease that degrades C3 into inactive fragments + Preclinical NHP PK & PD data* predict

best-in-class human intravitreal dosing three or four times a year Biogen collaboration + Announced December 19, 2019 + $15M upfront, up to

$340M in milestones and tiered royalties up to low double digits + Catalyst to perform fully funded pre-clinical and manufacturing activities + Biogen responsible for

IND-enabling activities, worldwide clinical development & commercialization *Furfine et al. ARVO 2019 Catalyst Biosciences

CB 4332 SQ long-acting systemic complement regulator Non-human primate PK supports weekly SQ

dosing in humans level Plasma Parent Molecule Functional Improvements Days Expanding the complement portfolio + Leverages Catalyst s proprietary protease engineering platform + Designed for SQ administration & improved bioavailability

+ Simple & efficient production process + Program update in Q4 Catalyst Biosciences

Milestones 2020 Q1 2020 EoP2 Interim P2b NextGen vector Q2 2020 ToB PK/PD Final P2b NHP efficacy Q3 2020 MAA-102 data Population PK Q4 2020 Enroll pivotal P3 Initiate P1/2 in FVII deficiency, Glanzmann Thrombasthenia, and Hemlibra patients Initiate pivotal NHP study Development candidate MarzAA DalcA CB 2679d-GT CB 2782-PEG CB DC (FVIIa) (FIX) (FIX gene therapy) (dAMD) (Systemic complement) Catalyst Biosciences

Team Nassim Usman, Ph.D. President & CEO 28 years in biotech Clinton Musil, M.B.A Chief Financial Officer 16 years in

biotech & investing/banking Howard Levy, M.B.B.Ch., Ph.D. Chief Medical Officer 20 years in hematology Grant Blouse, Ph.D. SVP Translational Research 13 years in biotech Jeffrey Landau, M.B.A. SVP Business Development 18 years in biotech