Stealth BioTherapeutics : Investor Presentation January 2021

Targeting bioenergetic dysfunction across human disease

January 2021

Our forward-looking statements and disclaimers

This presentation and various remarks we make during this presentation contain forward-looking statements within the meaning of The Private Securities Litigation Reform Act of 1995. Such forward-looking statements include those regarding Stealth BioTherapeutics' plans, strategies and expectations for its preclinical and clinical advancement of its drug development programs including elamipretide, SBT-20,SBT-272,SBT-259 and SBT-550; the potential benefits of Stealth BioTherapeutics' product candidates; its key milestones for 2021; its plans regarding future data presentations; and its financial guidance regarding the period in which it will have capital available to fund its operations. The words "anticipate," "expect," "hope," "plan," "potential," "possible," "will," "believe," "estimate," "intend," "may," "predict," "project," "would" and similar expressions are intended to identify forward-looking statements, although not all forward-looking statements contain these identifying words. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in the forward-looking statements we make as a result of known and unknown risks, uncertainties and other important factors, including: our ability to obtain additional funding; the ability to successfully demonstrate the efficacy and safety of Stealth BioTherapeutics' product candidates and future product candidates; the preclinical and clinical results for Stealth BioTherapeutics' product candidates, which may not support further development and marketing approval; the potential advantages of Stealth BioTherapeutics' product candidates; the content and timing of decisions made by the U.S. FDA, the EMA or other regulatory authorities, investigational review boards at clinical trial sites and publication review bodies, which may affect the initiation, timing and progress of preclinical studies and clinical trials of Stealth BioTherapeutics product candidates; Stealth BioTherapeutics' ability to obtain and maintain requisite regulatory approvals and to enroll patients in its planned clinical trials; unplanned cash requirements and expenditures; competitive factors; Stealth BioTherapeutics' ability to obtain, maintain and enforce patent and other intellectual property protection for any product candidates it is developing; and general economic and market conditions. These and other risks are described in greater detail under the caption "Risk Factors" included in the Stealth BioTherapeutics' Annual Report on Form 20-F for the year ended December 31, 2019 filed with the Securities and Exchange Commission on April 1, 2020 and any future filings with the Securities and Exchange Commission. Any forward-looking statements contained in this presentation and various remarks we make during this presentation speak only as of the date hereof, and Stealth BioTherapeutics expressly disclaims any obligation to update any forward-looking statements, whether as a result of new information, future events or otherwise, except as required by law.

2 © 2021 Stealth BioTherapeutics.

Pioneering mitochondrial medicine

Cardiology platform

Remodeling the failing heart

• Barth NDA submission early 2021
• FRDA P2a commencing H1 2021
• DMD P2/3 planning

3 © 2021 Stealth BioTherapeutics.

Ophthalmology platform

Improving vision in blinding diseases

• Dry AMD Phase 2b data early 2022
• FRDA P2a also assessing vision
• LHON P3 pending formulation decision
• IVT formulation development ongoing

Neurology platform

Evidence of peripheral improvements

Early signs of neuronal protection

• Replisome Myopathy P3 planning
• ALS/MSA preclinical evidence of

neuronal protection with SBT-272

• Differentiated pipeline SBT-550

series targets ferroptosis pathway

Our pipeline

Cardiology

Ophthalmology

Neurology

Indication	Drug	Discovery	Preclinical	Phase 1	Phase 2	Phase 3
Barth Syndrome	Elam
Duchenne cardiomyopathy	Elam					Initiate P2 study H2 2021
Friedreich's ataxia (FRDA)	Elam					Initiate P2a study H1 2021
Dry age-related macular	Elam
degeneration (AMD)
Leber's hereditary optic neuropathy	Elam
(LHON)								Initiate P3 study
Replisome myopathies	Elam
						H2 2021

ALS/MSA/neuro	SBT-
272
Other neuro	SBT-
550

4 © 2021 Stealth BioTherapeutics.