Fundraising Fox
John Brennan
InvestorManaging Partner at Holly Ventures
San Francisco Bay Area
Writes $200K – $5M checks · typically $2M
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About
John Brennan founded and manages Holly Ventures, focusing on supporting early-stage cybersecurity entrepreneurs. He previously worked at YL Ventures, DCVC, OCA Ventures, and Horsley Bridge Partners, and holds an MBA from the University of Chicago and a BS from Trinity College in Connecticut.
Invests in
AI & Machine LearningCybersecurityDeveloper ToolsEnterprise SoftwareSaaS
Deals · 5
AsteliaSolo GP
via Holly Ventures · filed Feb 2026
Beacon SoftwareSolo GP
via Holly Ventures
CiderSolo GP
via Holly Ventures
TalononeSolo GP
via Holly Ventures
VeniceSolo GP
via Holly Ventures
Attribution from SEC filings, press coverage, and firm rosters. Some rows are inferred. Not right? Tell us.
Other disclosed investments
Investor
build.securityEureka SecurityOpus SecuritySperaValence SecurityVulcan Cyber
Per curated public sources.
Frequently asked questions
- Who is John Brennan?
- John Brennan founded and manages Holly Ventures, focusing on supporting early-stage cybersecurity entrepreneurs. He previously worked at YL Ventures, DCVC, OCA Ventures, and Horsley Bridge Partners, and holds an MBA from the University of Chicago and a BS from Trinity College in Connecticut.
- Where does John Brennan work?
- John Brennan is Managing Partner at Holly Ventures.
- What does John Brennan invest in?
- John Brennan invests in AI & Machine Learning, Cybersecurity, Developer Tools, Enterprise Software, SaaS.
- What check size does John Brennan write?
- John Brennan typically writes checks of $200K – $5M.
- What companies has John Brennan invested in?
- Investments tracked here include build.security, Eureka Security, Opus Security, Spera, Valence Security, Vulcan Cyber.
About this profile. Compiled from public sources — Holly Ventures's own website and public professional profiles — and summarised by Fundraising Fox; every fact is kept with where it came from. Spotted an error, or would rather not be listed? Email privacy@fundraisingfox.com · How we build profiles · Your rights