Junior Machine Learning Engineer

Join to apply for the Junior Machine Learning Engineer role at Trainline.

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 an 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.

Machine Learning is at the heart of Trainline’s mission to help millions of people make sustainable travel choices every day. Our ML models power critical aspects of our platform, including:

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• Advanced search and recommendation capabilities across our mobile and web applications
  
• Pricing and routing optimisations to find the best fares for customers
  
• Personalised user experiences enhanced by RL agents & generative AI
  
• Data‑driven digital marketing systems
  
• AI agents improving customer support
  

We are looking for a Junior Machine Learning Engineer to join our team and help shape the future of train travel. You will be part of a highly innovative AI and ML platform working alongside engineers, scientists and product managers to tackle complex challenges by combining Trainline’s rich datasets with cutting‑edge algorithms. What unites our team is an expertise in the field, a love of what we do and the desire to create impactful solutions to support Trainline’s goals of encouraging sustainable travel. As a part of Trainline you will be joining an environment where learning and development is top priority. You will have the opportunity to work with fellow ML enthusiasts on large‑scale production systems, delivering highly impactful products that make a difference to our millions of users.

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• Work in cross‑functional teams combining data scientists, software, data and machine learning engineers, and product managers
  
• Design and deliver machine learning models at scale that drive measurable impact for our business
  
• Own the full end‑to‑end machine learning delivery lifecycle including data exploration, feature engineering, model selection and tuning, offline and online evaluation, deployments and maintenance
  
• Work with the MLE Team and stakeholders to help design and deliver data‑driven products using Trainline’s extensive datasets and modern machine learning techniques
  
• Create the tools, frameworks and libraries that enable the acceleration of our ML product delivery and improve our workflows
  
• Take an active part in our AI and ML community and foster a culture of rigorous learning and experimentation
  

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• Have an advanced degree in Computer Science, Mathematics or a similar quantitative discipline
  
• Are proficient with Python, including open‑source data libraries (Pandas, Numpy, Scikit‑Learn, etc.)
  
• Have experience productionising machine learning models
  
• Are an expert in predictive modelling, classification, regression, optimisation or recommendation systems
  
• Have experience with Spark
  
• Have knowledge of DevOps technologies such as Docker and Terraform, and MLOps practices and platforms like MLflow
  
• Have experience with agile delivery methodologies and CI/CD processes and tools
  
• Have a broad understanding of data extraction, manipulation and feature engineering techniques
  
• Are familiar with statistical methodologies
  
• Have good communication skills
  

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• Understanding and/or hands‑on experience of reinforcement learning theories, frameworks, and algorithms
  
• Experience with cloud infrastructure
  
• Experience with large language models (fine‑tuning, RAG, agents)
  
• Experience with graph technology and/or algorithms, understanding of NLP algorithms
  

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• Python and associated ML/DS libraries (scikit‑learn, NumPy, LightGBM, Pandas, TensorFlow, etc.)
  
• PySpark
  
• AWS cloud infrastructure: EMR, ECS, Athena, etc.
  
• MLOps/DevOps: Terraform, Docker, Airflow, MLflow, NewRelic
  

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• Recruiter Call (30 minutes)
  
• Meeting with a Machine Learning Manager (30 minutes)
  
• Technical interview with 2 x Engineers (90 minutes)
  
• Final interview with the Head of (30–45 minutes)
  

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!

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• 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. We are committed to creating inclusive places to work, where everyone belongs and differences are valued and celebrated.

Location: London, England, United Kingdom

Salary: $100,000.00 – $200,000.00

If you’re excited to join Trainline and make sustainable travel accessible for all, send us your application today.