Senior/Staff Product Engineer (Mobile) at Joinfleek - a16z-backed marketplace

As a Senior/Staff Product Engineer, you will own the mobile experience for the world's fastest-growing wholesale secondhand fashion marketplace. Joining the London-based Demand team, you will build the primary interface used by 90% of buyers, integrating AI-driven classification into a seamless, high-performance React Native application that directly drives global GMV.

• Lead the development of the core React Native application, focusing on high-polish discovery, browsing, and purchasing flows that convert intent into transactions.
• Partner with data and AI teams to implement mobile surfaces for the FleekSort classification engine, making complex AI grading feel intuitive for users.
• Build and maintain a robust experimentation framework for A/B testing and analytics to drive data-informed product decisions and optimize conversion rates.

• 4–10+ years of professional software engineering experience with deep, production-level expertise in React Native and mobile performance optimization.
• Proven track record in a fast-paced consumer marketplace or e-commerce environment where interaction quality and animation polish are treated as core features.
• Product-minded engineer who leverages AI tools like Cursor or Copilot and connects technical trade-offs to commercial outcomes rather than just following tickets.

• Direct ownership of the #1 revenue channel for a hyper-growth startup tripling year-on-year with backing from top-tier VCs like a16z and Y Combinator.
• High-impact architectural influence where you define the mobile standards and experimentation layers for a marketplace disrupting a fragmented supply chain across 70+ countries.
• Work in an AI-first engineering culture under leadership from Google and Postmates, utilizing cutting-edge tools to solve complex inventory and discovery challenges.