Principal Machine Learning Scientist

Principal Machine Learning Scientist London | Hybrid | Senior Individual Contributor Are you excited by search, ranking and recommendation systems at scale? Do you enjoy turning complex product challenges into elegant, production-ready ML architecture? Our client is a major digital platform hiring a Principal Machine Learning Scientist to shape the technical direction for intelligent discovery, planning and personalisation across a large-scale marketplace environment. This is a hands-on technical leadership role, not a people management position. You will define architecture, raise engineering and ML standards, coach strong technical teams and help turn complex product challenges into scalable production systems. Why This Role is Great You will have the chance to:

• Shape the ML vision for search, discovery and planning products.
• Design advanced retrieval, ranking and recommendation systems.
• Work with sequential modelling, embeddings, semantic retrieval and multimodal learning.
• Influence MLOps, experimentation, system design and production quality.
• Partner closely with Product, Data and Engineering leaders.
• Coach and mentor other ML specialists while staying deeply technical. About You You will likely bring strong experience in:
• Building and deploying large-scale ML systems in production.
• Machine learning for search, ranking, recommendations or personalisation.
• Multi-objective optimisation, such as MTL, MMoE or similar approaches.
• Sequential recommendation systems, temporal modelling or session-based modelling.
• Representation learning, embeddings, semantic retrieval or multimodal ML.
• Python and frameworks such as PyTorch or TensorFlow.
• Cloud and distributed computing using technologies such as AWS, GCP, Spark or Ray.
• Working with systems operating at significant user and data scale. A Master's or PhD in Computer Science, Machine Learning, Statistics or another highly quantitative field is preferred, alongside around 8+ years of relevant industry experience. Experience with graph-based ML, knowledge graphs, Agentic AI or Generative AI would also be useful, as would experience within e-commerce, marketplaces or similarly complex digital products. Location This role is based in London, with hybrid working and around one day per week in the office. Apply If your background is in large-scale search, ranking or recommendation systems and you're looking to stay deeply technical while having Principal-level influence, we'd be keen to hear from you.