Principal Software Engineer, Mobile (React Native)

Nine Elms, London - Full-time (4 days a week on-site)

About Zapp

Zapp is London’s leading premium convenience retail platform. Founded in 2020, our vision is to disrupt the multi-trillion dollar convenience retail market, currently dominated by major players, by developing best-in-class customer-centric technology and fulfilment solutions. Zapp partners with some of the world’s leading brands to deliver an exclusive range of hand-picked products 24/7, delivered in minutes.

Quick commerce is a genuinely hard mobile problem. Stock changes by the second, orders and riders move in real time, and we make sub-minute promises we have to keep, all on patchy high-street connections across a huge range of devices. Getting that right, fast and reliably, is the job.

We are serious about AI, as a way of working rather than a slogan. AI-assisted development is part of the daily toolkit here, and we ship LLM-powered features where they genuinely make the product better.

The Role

As Principal Mobile Engineer you own the technical direction of our consumer iOS, Android and web apps, all built on React Native. This is a deliberately hands-on Principal role. You set the architecture and the standards, and you are still in the code every week shipping the hardest parts yourself. You will be the most senior mobile engineer in the company and the person the rest of the team levels up against.

You will work closely with stakeholders in Commercial, Marketing and Operations to shape what we build and make sure the app serves the whole business.

What you'll do

• Own the architecture of the React Native app across iOS, Android and web, and make the calls on patterns, tooling and technical direction

• Stay hands-on: ship the hardest features yourself and set the standard for what good looks like in the codebase

• Raise the engineering bar across the mobile team through sharp code review, mentoring, and the example you set

• Drive performance, stability and responsiveness, profiling and fixing the things that actually hurt on real devices and real networks

• Own the release process and the health of what we put in front of customers

• Partner with the wider business and the leadership team to turn ideas into fast, reliable, polished experiences

• Work across the stack where it helps, into the backend APIs and data layers that feed the app

• Use AI tooling (Claude, Cursor, Copilot) to ship faster and help the team get genuinely good at it, and build AI-powered features with LLM and on-device capabilities where they improve the product

What you'll bring

Essentials

• A track record of building and shipping B2C consumer mobile apps at scale, and being the person who sets technical direction for a mobile team

• Deep React Native expertise across iOS and Android, with the judgement to know its limits and drop into native when needed

• Strong TypeScript

• Real command of mobile performance, stability and release processes

• Solid grasp of mobile security: secure storage, authentication patterns, and API security

• You take genuine end-to-end ownership and operate autonomously

• You communicate clearly, in writing and in person, and can bring people with you on a technical call rather than just winning the argument

You have probably been doing this for 7 or more years, but we care about the impact you have had, not the number on your CV.

Nice to have

• Node.js (Express, Fastify) for the API layer

• React.js or React Native for Web

• Native experience (Kotlin, Swift) for the bridge and the trickier native modules

• GraphQL, GCP, Firestore, Event-Driven architecture

• Hands-on experience building with LLM or AI APIs

Benefits

• Competitive salary, plus meaningful equity

• 25 days holiday, plus all bank holidays

• Private health insurance

• Extended sick pay and enhanced maternity and paternity leave

• Cycle to work scheme