Senior Principal Engineer (iOS)

About us

We are champions of rail, inspired to build a greener, more sustainable future of travel. Trainline enables millions of travellers to find and book the best value tickets across carriers, fares, and journey options through our highly rated mobile app, website, and B2B partner channels. 

Great journeys start with Trainline 🚄 

Now Europe’s number 1 downloaded rail app, with over 135 million monthly visits and £6.3 billion in annual ticket sales, we collaborate with 270+ rail and coach companies in over 40 countries. We want to create a world where travel is as simple, seamless, eco-friendly and affordable as it should be. 

Today, we're a FTSE 250 company driven by our incredible team of over 1,000 Trainliners from 50+ nationalities, based across London, Paris, Barcelona, Milan, Edinburgh and Madrid. With our focus on growth in the UK and Europe, now is the perfect time to join us on this high-speed journey. 

Introducing the Trainline App Platform Team 👋
The App Platform team provides the foundations that enable our mobile engineering teams to build, evolve and deliver exceptional customer experiences at scale. Working across iOS and Android, the team develops the shared capabilities, tooling, frameworks and engineering practices that help product teams move faster while maintaining high standards of quality, performance and reliability.

As our Senior Principal Engineer (iOS), you will play a pivotal role in shaping the future of iOS engineering at Trainline. While embedded within the App Platform team, your influence will extend across the wider technology organisation as you define the long-term technical strategy for iOS alongside peers across Android, Web and Architecture. You'll establish a cohesive cross-platform architectural vision, balancing platform-specific innovation with opportunities to simplify solutions, increase consistency and avoid unnecessary duplication. This is a highly influential individual contributor role where you'll create leverage through technical leadership, partnering with engineers, architects, product, design and senior leaders to solve complex challenges, shape engineering strategy and raise the technical bar across the organisation.

In this role as the Senior Principal Engineer (iOS), you will...🚄

• Define and own the long-term technical strategy for iOS, ensuring it supports Trainline's business goals while aligning with the wider architectural vision across mobile, web and platform engineering.

• Own and evolve engineering standards, reusable patterns and best practices for iOS across Trainline, creating greater consistency, improving developer experience and enabling teams to build high-quality software more effectively.

• Lead organisation-wide technical modernisation programmes that simplify our engineering landscape, improve maintainability and scalability, and enable product teams to deliver faster with confidence.

• Partner closely with Principal Engineers, Architects and senior engineering leaders to establish a cohesive cross-platform strategy, identifying opportunities to share capabilities and architectural approaches while making pragmatic decisions about where platforms should remain distinct.

• Champion technical excellence through modular, testable and maintainable software design, helping engineering teams adopt practices that improve quality, reliability, performance and long-term sustainability.

• Evaluate emerging technologies and AI-enabled engineering practices, identifying where they create meaningful value for developers and customers while balancing innovation with security, operational cost and long-term sustainability.

• Influence technical direction across the engineering organisation through clear communication, compelling technical proposals and trusted relationships with engineers, architects, product, design and executive stakeholders.

• Mentor and develop senior engineers and members of the Principal Engineering community, while representing Trainline within the wider engineering community through knowledge sharing, technical leadership and community engagement.

We'd love to hear from you if you have...🔍

• Significant experience defining technical strategy for large-scale iOS platforms or products, with a track record of delivering architectural improvements that have created lasting impact across multiple teams or organisations.

• Deep expertise in modern iOS development, alongside strong experience designing modular, testable and maintainable software that balances scalability, reliability, performance and long-term maintainability.

• Experience establishing engineering standards, technical patterns and best practices, with the ability to influence their adoption across an organisation through technical credibility and collaboration.

• A proven ability to create alignment across engineering disciplines, working closely with architects, product, design and technology leaders to develop shared technical direction and deliver business outcomes.

• Strong judgement when evaluating emerging technologies, including AI-enabled engineering capabilities, with the ability to identify where they can create genuine value while balancing cost, risk and long-term sustainability.

• Excellent communication and influencing skills, with the ability to adapt your style to engage audiences ranging from hands-on engineers to senior and executive stakeholders.

• Have an active presence within the wider iOS engineering community through speaking, mentoring, open-source contributions or community engagement, although this is not essential.

More information:

Enjoy fantastic perks like private healthcare & dental insurance, a generous work from abroad policy, 2-for-1 share purchase plans, an EV Scheme to further reduce carbon emissions, extra festive time off, and excellent family-friendly benefits. 

We prioritise career growth with clear career paths, transparent pay bands, personal learning budgets, and regular learning days. Jump on board and supercharge your career from day one! 

We're operating a hybrid model and ask that Trainliners work from the office a minimum of 60% of their time over a 12-week period. We also have a 28-day Work from Abroad policy.

Our values represent the things that matter most to us and what we live and breathe everyday, in everything we do: 

• 💭 Think Big - We're building the future of rail 

• ✔️ Own It - We focus on every customer, partner and journey 

• 🤝  Travel Together - We're one team 

• ♻️ Do Good - We make a positive impact 

We know that having a diverse team makes us better and helps us succeed. And we mean all forms of diversity - gender, ethnicity, sexuality, disability, nationality and diversity of thought. That's why we're committed to creating inclusive places to work, where everyone belongs and differences are valued and celebrated.

Interested in finding out more about what it's like to work at Trainline? Why not check us out on LinkedIn, Instagram and Glassdoor!