Senior Product Security Engineer in London

About 9fin: 9fin is the AI platform powering global debt markets — the world’s largest asset class at over $145 trillion. Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets. Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption.

The Opportunity: We’re looking for a Senior Product Security Engineer to join one of our software engineering teams and help shape the security of our products as we continue to scale. This role will be embedded within a team responsible for some of the most security-critical parts of the 9fin platform. The team works on the systems and controls that protect sensitive customer information, ensuring data is stored, accessed and processed securely throughout its lifecycle.

You’ll work alongside product engineers day-to-day, participating in planning, design discussions, refinement sessions and technical decision-making. You’ll help the team make sound architectural decisions about how sensitive information is stored, processed and accessed, balancing security requirements with product and engineering goals. The team operates at the intersection of application security, cloud security, data protection and AI security. You’ll help shape how 9fin approaches challenges such as tenant isolation, access control, confidential data handling and the secure use of AI systems. While embedded within product engineering, you’ll remain closely connected to our Platform Engineering and Information Security teams, helping drive a consistent approach to security across 9fin.

This is a hands-on engineering role. You won’t be building product features full-time, but you should be comfortable reading, reviewing and writing production code when security requirements demand it.

What you'll work on:

• Embed within a product engineering team and help shape the security of our products from design through to production.
• Influence architecture, design and implementation decisions to ensure security is considered from the outset.
• Partner with Product Engineering, Platform Engineering and Information Security teams to identify risks, define appropriate controls, and build secure-by-default systems.
• Contribute code, reviews and technical guidance where security expertise is required.
• Act as a security advocate and trusted advisor within the team, helping balance risk, usability and delivery.

What we’re looking for:

• Significant experience securing modern software systems and applications.
• Strong understanding of secure software architecture, threat modelling and security engineering practices.
• Deep familiarity with cloud-native architectures and security controls, particularly within AWS.
• Experience designing systems that handle sensitive, confidential or regulated data.
• Comfortable reading, reviewing and writing production code, ideally with experience in Python or similar backend technologies.
• Familiar with the security considerations of modern data stores such as PostgreSQL.
• Pragmatic judgement and the ability to balance security, product and engineering needs.
• Ability to influence engineers and stakeholders across multiple teams without relying on formal authority.
• Familiarisation with SOC2 and ISO 42001 is a bonus.

What success looks like:

• Security considerations are embedded into product design discussions rather than introduced late in the delivery process.
• Teams can move quickly because secure patterns, architectural guidance and security controls are well understood.
• Risks are identified and addressed before they become incidents.
• Security is seen as an enabler of product delivery rather than a gatekeeper.

Why this role matters: Security cannot be something that happens after software has been designed. As 9fin continues to expand its platform and handle increasingly sensitive customer information, we need security expertise embedded where decisions are being made. This role will help ensure that security is considered from the earliest stages of product development, allowing us to move quickly while maintaining the trust our customers place in us.

Benefits: We’re a scaling start up and we enjoy sharing our success; when the company succeeds, we always reinvest that in our people. We also offer huge amounts of responsibility, an abundance of opportunity for growth and a platform to truly excel.

Financial & Insurance:

• Competitive Salary (our salary bands are benchmarked at the top end of the market)
• Equity options
• Pension (your minimum contributions are 4% with 9fin matching up to 7%)
• Private Medical Insurance
• Paid sick leave with Income Protection for long periods of illness
• Group Life Assurance
• Season Ticket Loan & Cycle to Work schemes

Time off:

• 25 holiday days per year
• Local public holidays (with the ability to exchange them for alternative days)
• Hybrid working model, to allow you the flexibility to decide how, where and when you do your best work
• Work abroad for up to 3 months a year
• 1 month paid sabbatical after 5 years of service
• Enhanced parental leave & flexible working arrangements available

Training & Culture:

• Professional learning and development budget
• Quarterly team socials
• Summer and Winter company social events

9fin is an equal opportunities employer. At 9fin we are dedicated to building and promoting a fair and inclusive workplace where everyone can reach their full potential and truly belong. We recognize that building diverse teams enables a more creative and productive environment. If you’re excited about this role but your experience doesn’t perfectly align with the job description, we encourage you to apply anyway. You might just be who we’re looking for — either for this role, or perhaps another.