Machine Learning Engineer - Gen AI

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'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 Machine Learning & AI at Trainline 👋

Machine learning is at the heart of Trainline’s mission to help millions of customers make sustainable travel choices every day. Within our AI & ML community, we build and operate production-grade systems that power search, pricing, personalisation, marketing optimisation, and increasingly, intelligent AI agents that transform customer support and journey discovery.

You’ll join a cross-functional team of Machine Learning Engineers and Data Engineers working on some of our most exciting GenAI initiatives. We’re building agentic systems such as our Travel Assistant, an AI-powered experience that helps customers with refunds, journey updates, and ticket conditions and expanding into Voice AI agents to intelligently handle and redirect customer queries.

This is a team that combines strong ML fundamentals with cutting-edge LLM frameworks (LangGraph, LangChain), RAG architectures, MCP integrations, and production monitoring tools like Braintrust, all deployed on AWS. We value ownership, curiosity, and thoughtful experimentation in a healthy, supportive environment.

About The Role

This role is focused on designing, building, and operating LLM-powered and predictive ML systems in production. You’ll work on agentic AI systems, including our Travel Assistant and Voice AI initiatives, while also contributing to more traditional ML services that the team owns.

If you’re passionate about GenAI, LLMs, NLP, and shipping robust ML systems end-to-end, this is an opportunity to work at the forefront of applied AI in a high-impact consumer platform.

As a Machine Learning Engineer at Trainline, you will... 🚝

• Design and build LLM-powered agentic systems using frameworks such as LangGraph and LangChain
• Develop and optimise RAG pipelines, tool-using agents, and multi-step workflows with appropriate guardrails and validation
• Monitor and evaluate model and agent performance using appropriate ML metrics (e.g. precision, recall) and production monitoring tools
• Maintain and improve traditional ML models alongside newer GenAI capabilities
• Partner closely with stakeholders to frame problems, define success metrics, and deliver measurable business impact
• Take ownership of technical initiatives, driving delivery from ideation through to production and iteration

Contribute to our wider AI & ML community through knowledge sharing, experimentation, and continuous learning

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

• Have strong experience in Machine Learning with solid foundations in the ML lifecycle, evaluation methodologies, and statistical thinking
• Have hands-on experience with GenAI, Large Language Models, and NLP techniques, including RAG and agent-based systems
• Are proficient in Python and common ML libraries (e.g. PyTorch, scikit-learn, XGBoost, Pandas)
• Have experience deploying and operating ML or AI systems in production environments
• Understand ML Ops and DevOps principles (e.g. Docker, CI/CD, infrastructure as code)
• Have experience working with cloud infrastructure (preferably AWS)
• Take ownership of technical tasks and proactively drive solutions forward
  
  

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 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 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!