Fleek is a UK-based startup operating an AI-powered B2B marketplace and AI infrastructure for wholesale secondhand clothing suppliers, retailers and resellers.
Can you help us fix the world's most broken supply chain? The fashion industry produces over 100 billion garments a year. 60% end up in landfill, not because people don't want these clothes, but because the supply chain for getting secondhand fashion from donation to resale is completely offline, manual, and broken. Fleek is fixing this. Our mission is to make secondhand the first choice. We're building the infrastructure powering the global secondhand clothing trade, through a B2B marketplace and the AI systems digitising the supply chain behind it. Through Fleek, vintage stores, online resellers, and retail buyers source graded secondhand inventory directly from wholesalers and rag houses across multiple countries. Our key enabler is FleekSort, an AI model fine-tuned on secondhand fashion, that can grade, price, and categorise items with just a photo, turning what has historically been an opaque and manual trade into a structured, searchable, and tradable global inventory layer. Since 2022, we've saved 9 million items from landfill while tripling in size year-on-year. We're backed by some of the world's best investors, including a16z, Y Combinator, and HV Capital, alongside world-class angels who helped build Depop, Shopify, and Postmates. Today, we serve thousands of resellers and retailers across the UK, Europe, and the US. With the secondhand fashion market projected to reach $350B by 2027, Fleek is building the AI-native operational and financial backbone for secondhand commerce globally. We're looking for people who want to build something that matters, and move fast doing it. Sound good? Keep reading. About the Role This is a Senior Product Engineer (backend) role in Fleek's product engineering team. You'll report into our CTO, Sanket Agarwal (ex-Google, Postmates), and work embedded with a product manager and designer in a small, senior squad focused on the core marketplace experience. Why This Role Stands Out Fleek is digitising an industry that has never had technology. There are no existing playbooks for building an ecommerce experience around secondhand fashion at wholesale scale, where every item is unique, inventory is unpredictable, quality is graded by AI, and the supply chain spans three continents. You will be designing how the transaction layer works for a market that hasn't existed before. You will be on our Growth team, owning the ecommerce journey from discovery to checkout, payment and credit systems, order management, and seller tools. Your systems will handle 500,000+ items a month today and million+ by the end of the year. AI is at the core of everything we do, so you'll work closely with our data and AI teams to build the backend services that connect FleekSort's classification engine to the marketplace experience. We're looking for a product engineer who can think about how systems affect buyers and sellers at scale. You'll be expected to understand the business problems your code solves, and challenge whether we're solving the right ones. What Makes You a Fleek Product Engineer? - Product-Obsessed Builder: You think about what the seller sees when their inventory goes live, or why a buyer drops off at checkout. You instinctively connect technical decisions to commercial outcomes. - Comfortable with Ambiguity: We're building systems for workflows that didn't exist before Fleek. You thrive when the problem is undefined and collaboration is key. - Customer-Focused Thinker: You understand the dynamics of customer platforms and can understand how technical choices affect customers and our broader marketplace. - Owner, Not Renter: You take a feature from problem definition to production and monitor it afterwards. - Startup Pace: You've worked in environments where shipping matters more than perfection, where you deploy daily, and where velocity is a competitive advantage. What You'll Do - Own the Ecommerce Journey: Design and build the backend systems powering Fleek's core marketplace, from item discovery and search through to checkout, payment, and post-purchase. These are product features that directly drive GMV. - Integrate AI into the Product: Build the services that connect FleekSort's AI classification engine to the marketplace experience, ensuring grading, pricing, and categorisation flow seamlessly into listings, search, and buyer workflows. - Design for Scale: Architect systems that handle 500K+ items per month today, with a clear path to millions. Make pragmatic trade-offs between speed of delivery and long-term scalability. - Shape Technical Direction: Contribute to architectural decisions across the backend. Challenge assumptions, propose alternatives, and help define engineering standards for a fast-growing team. - Mentor and Elevate: Support the growth of more junior engineers through code reviews, pairing, and knowledge sharing. Help raise the technical bar across the team. - Collaborate Cross-Functionally: Work embedded with your product manager and designer to define what gets built. Partner with data, AI, and operations teams to turn complex real-world logistics into reliable, scalable software. What You Bring - 3–6 years of professional backend engineering experience You've built and shipped production systems that handle real traffic and real money. - Strong fundamentals in system design, data modelling, and API architecture. You can design a service from scratch and reason about its failure modes before you write a line of code. - Experience with Node.js and TypeScript (our primary backend stack), or strong proficiency in a comparable stack with willingness to transition. - Consumer tech background. You've worked at a marketplace, fintech, or consumer product company. You understand what it means to build for end users at scale, not internal tooling or enterprise workflows. - Product engineering mindset. You can articulate the business problem your code solves. You've worked closely wit