Principal Data Engineer

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 125 million monthly visits and £5.9 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 are 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 Data Engineering team at Trainline. Principal Data Engineers at Trainline are senior technical leaders who operate across multiple teams, embedding best practices, raising engineering standards, and enabling our most ambitious data, ML and AI initiatives. You will actively seek out the highest-impact problems across multiple cross-functional squads, partnering closely with Machine Learning Engineers (MLEs), ML Engineering Managers, Product and Platform teams to ensure we build robust, scalable and future-proof data foundations for ML-driven products such as the Travel Assistant. Embedded Data Engineering (Embedded DE) is a core part of this role. You will work inside ML-led teams, shaping architecture, guiding implementation, and ensuring alignment between Data Engineering and ML Engineering best practices across Trainline.

As a Principal Data Engineer, you will:

• Act as a technical authority across multiple teams, setting standards and patterns for data and ML-adjacent infrastructure
• Embed with ML teams to design, build and evolve data platforms supporting AI and ML workloads
• Influence technical direction without direct line management responsibility
• Partner with Data Engineering teams outside of ML to build a community and share best practices and findings across all areas
• Identify systemic issues and proactively drive improvements across the data ecosystem
• Look for short term and strategic opportunities to enhance core platforms with new self-serve enablement features for ML and DE

Your typical day may include:

• Partnering with MLEs to design data pipelines supporting model training, inference and experimentation
• Designing and reviewing architectures for ML-ready data platforms
• Building and optimising data pipelines using SQL, Spark or Ray and Python
• Defining best practices for orchestration using Airflow or similar tools
• Supporting API-driven and event-based data access patterns
• Working with AWS infrastructure such as ECS, vector databases and Bedrock APIs
• Reviewing designs and code across teams to raise quality and consistency
• Coaching engineers through pairing, design reviews and informal mentoring
• Collaborating on innovative AI-powered product features such as the Travel Assistant

We'd love to hear from you if you have:

• Extensive experience as a Senior, Staff or Principal Data Engineer operating across teams
• Deep expertise in SQL and Python, with strong experience in Spark or similar tooling
• Strong understanding of orchestration tools such as Apache Airflow
• Experience designing data platforms for ML and AI workloads
• A track record of introducing new technologies and practices, and handling ambiguity and multiple stakeholders
• Hands-on experience with AWS infrastructure (e.g. ECS, IAM, data storage, compute)
• Familiarity with vector databases and modern AI/ML APIs (e.g. Bedrock)
• Experience working closely with Machine Learning Engineers in production environments
• Strong system design skills and the ability to influence through technical leadership

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 operate a hybrid model to work 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 every day, 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!