Senior Full Stack Engineer

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 Full Stack Engineer role in Fleek's product engineering team, with a frontend lean. 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 user growth and the core consumer experience.

Why This Role Stands Out

Fleek is building a social, video-first marketplace where every item is unique, supply is unpredictable, and the buying experience has to work for professional resellers making high-volume purchasing decisions and first-time buyers exploring a market they've never seen before.

You will be on our Growth team, rebuilding core user journeys from first principles, the discovery experience, the buying flow, seller onboarding, and the mobile app that's becoming an increasingly critical surface. You'll run your own experiments, interrogate your own data, and ship features that move metrics you can see. When you improve activation by 5%, you'll watch it in the revenue numbers the same week.

The platform handles 500,000+ items a month across web and mobile today and million+ by the end of the year, with AI-powered grading and pricing integrated throughout the experience. You'll work across both React (web) and React Native (mobile), and you'll be expected to reach into the backend when the feature demands it.

We're looking for a product engineer who thinks about user behaviour, commercial impact, and growth mechanics, and ships fast enough to test their hypotheses. 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 Full Stack Engineer?

• Growth-Wired: You think in funnels, activation loops, and conversion rates. You've shipped features that directly moved user acquisition, retention, or revenue, and you can point to the numbers.

• Design Partner: You work with designers, challenge UX decisions, and suggest improvements based on what you see in the data. You care deeply about how an experience feels.

• Customer-Focused Thinker: You've built for end users at scale. You understand how technical choices affect customers and the broader product experience.

• Experiment-Driven: You run A/B tests, track results, and let data inform your decisions. You're not precious about your code, if the experiment says it doesn't work, you move on.

• Full Stack Mentality: Your strength is the frontend, but you don't stop at the API. If the feature needs a backend change, you make it. If the data model is wrong, you flag it and propose a fix.

What You'll Do

• Own User-Facing Features End-to-End: Take features from problem definition through to production across web and mobile. Own the outcome, not just the output. Your work directly impacts GMV, activation, and retention.

• Rebuild Core Product Experiences: Redesign and re-engineer key user journeys, from item discovery and search through to the buying flow and post-purchase experience.

• Ship Growth Experiments: Build, run, and analyse A/B tests that drive user acquisition and activation. Run your own analytics queries, interpret results, and decide what to build next.

• Build Across Web and Mobile: Work in React (web) and React Native (mobile) to deliver a seamless experience across platforms. The mobile app is an increasingly critical surface and you'll help define its trajectory.

• Bridge Frontend and Backend: Reach into the Node.js/TypeScript backend when features require it. Extend APIs, improve data layers, and shape the systems behind the UI.

• Shape UX with Design: Collaborate closely with product and design to define what gets built. Challenge UX decisions with data. Bring technical constraints and opportunities into the design conversation early.

• Mentor and Elevate: Support more junior engineers through code reviews, pairing, and knowledge sharing. Help establish frontend engineering standards as the team grows.

What You Bring

• 3–6 years of professional frontend or full stack engineering experience. You've shipped consumer-facing products that real people use daily.

• Strong proficiency in React, with experience or strong interest in React Native. You understand component architecture, state management, and performance optimisation at scale.

• Backend capability. You're comfortable working in Node.js/TypeScript. You can build an API endpoint, write a database query, and understand how the systems behind the UI work.

• Data fluency. You can write SQL, set up and interpret experiments, and use metrics to inform product decisions.

• Consumer tech background. You've worked at a marketplace, social platform, fintech, or consumer product company. You know what it means to build for users at scale, with fast iteration cycles.

• Product engineering mindset. You can articulate the business problem your code solves. You've worked closely with product and design, and you've made trade-offs that balanced user experience with technical constraints.

• Startup or scale-up experience. You've worked in environments with fast deployment cycles, evolving requirements, and high ownership. You ship, learn, and iterate.

• Comfort with ambiguity. You don't need a detailed spec to start moving. You can take a problem statement and turn it into a working feature.

• AI first 10x-er. You think about your role as a 10x-er through the lens of AI. You've built AI capabilities either in your spare time or in deployment at scale.

Nice to Have

• Experience with growth engineering: experimentation platforms, A/B testing frameworks, funnel optimisation

• Familiarity with international systems and distributed teams across multiple time zones

A genuine excitement for building something from scratch in a category that didn't exist three years ago.

This Role Isn't for You If You Want:

• Pure UI-only work where you never touch business logic or data

• Detailed specs handed to you before you start, we define problems together

• A fully remote role, this team works from London 3–4 days a week and collaboration in person is central to how we operate

• A slow-moving, highly structured environment with long release cycles

• Narrow specialisation with no cross-stack exposure

Ready to build the infrastructure for the world's fastest-growing fashion economy? If you want to work on genuinely hard problems, with a world-class team, at a company that's tripling annually, we'd love to hear from you.

How We Work

Fleek is an in-office company. We believe the best work happens when people are together: the quick decisions, the cross-functional energy, the ability to solve problems in real time. Most of the team works from our London HQ 3–4 days a week.

We're not prescriptive about it. Performance and trust matter more than attendance. We hire adults and treat them accordingly.

The Practicalities

• Location: London HQ, Commercial St, E1 (Liverpool St / Aldgate East)

• Work model: In-office, typically 3–4 days per week.

• Level: Senior (L5)

• Stage: Post-Series B, hyper-growth

• Team: 100+ across London, India, and Pakistan

• Stack: React, React Native, Node.js, TypeScript

• Culture: High ownership, non-hierarchical, fast-moving. Founder-led with strong opinions loosely held.

Our Values

Five values shape how we work at Fleek:

• Dream Big and Disrupt Yourself: Push the most ambitious version of what you're building. Step out of your comfort zone. Nothing is out of reach.

• Absolute Ownership: The buck stops with you. Drive initiatives to completion. Experiment, learn, persevere. The job isn't done until the job is done.

• Curiosity Leads the Way: Don't accept anything at face value. Ask questions you don't know the answer to. That's how you innovate.

• Talk to the Customer: Deeply understand their challenges, motivations, and ambitions. Every decision starts with the customer at the centre.

• Embrace Diversity: A global team building for a global supply chain. Bring your authentic self and embrace the diversity of everyone you encounter.