Principal Machine Learning Engineer

Location: London, United Kingdom; role based at the hirify.global HQ in London.

Company

hirify.global is an online fashion retailer building digital shopping experiences for customers worldwide.

What you will do

• Own the technical architecture for machine learning systems powering personalized product and outfit recommendations, homepage ranking, search relevance, and AI Stylist experiences.
• Lead the design and evolution of large-scale batch and real-time ML systems serving millions of customers.
• Set technical direction across recommendation systems, retrieval, personalization, deep learning, generative AI, and intelligent product experiences.
• Translate research and experimentation into reliable, production-grade customer-facing ML products.
• Drive platform investment and build-versus-buy decisions while establishing architectural standards across teams.
• Mentor Senior and Staff engineers and communicate technical strategy to engineering, product, business, and technology stakeholders.

Requirements

• Extensive experience designing, building, and operating large-scale machine learning systems in production.
• Experience owning technical architecture across complex engineering ecosystems and influencing multiple teams without direct management responsibility.
• Deep expertise in at least two areas including ranking and relevance, recommendation systems, deep learning, large language models, information retrieval, natural language processing, or content understanding.
• Advanced hands-on experience with PyTorch, TensorFlow, or similar frameworks, plus strong programming skills in Python, Java, or C++.
• Strong understanding of MLOps, distributed infrastructure, cloud technologies, deployment, observability, monitoring, and lifecycle management.
• Experience with production AI systems using RAG, agent-based architectures, retrieval systems, model evaluation, and ML-driven scoring.

Nice to have

• Experience using AI-assisted engineering tools and coding agents such as Claude Code, Codex, Cursor, or similar technologies.
• Experience mentoring senior engineers and driving adoption of engineering standards across an organization.

Culture & Benefits

• 25 days of annual leave plus an additional celebration day.
• Employee discount, sample sales, private medical care, and a discretionary bonus scheme.
• Flexible benefits allowance and matched pension contributions of up to 5%.
• Personalized learning and career development opportunities.
• Summer hours with 3pm finishes on Fridays in June, July, and August.
• Office facilities include a gym, café, subsidized canteen, and shuttlebus service between Watford station and the Leavesden office.