Senior Full Stack AI Engineer

We are looking for a Senior Full Stack AI Engineer to join our AI team and help us build cutting‑edge legal solutions for some of the world’s largest law firms. In this role, you will leverage your deep expertise in machine learning, natural language processing, large language model (LLM) agents, and programming, alongside full‑stack development, to push the boundaries of legal technology. You’ll be collaborating closely with ML engineers, software engineers, and domain experts to integrate advanced NLP techniques into our products and deliver end‑to‑end user‑facing experiences.

You have strong front‑end (JS) and back‑end (Python, .NET, etc.) development skills, and are comfortable working across both backend systems and user‑facing interfaces, taking ownership of features from idea to production. It’s a role for someone who is comfortable working in a fast‑paced, sometimes ambiguous environment, enjoys solving complex problems, and wants to have a direct impact on product and technical direction.

What you’ll do:

• Designing and deploying LLM agents and agentic architectures to automate complex legal workflows
• Building and maintaining scalable, production‑grade systems that are reliable, secure, maintainable, and observable
• Working across the full stack to integrate AI capabilities into user‑facing products
• Owning features end‑to‑end, from prototyping through to production and iteration
• Collaborating closely with ML engineers, software engineers, and domain experts to bring AI‑driven features into the product
• Contributing to the direction of our AI initiatives by staying up to date with developments in NLP, machine learning, agentic systems, and full‑stack technologies

What you’ll bring:

• Experience working with LLMs in production and integrating ML/LLM components into product systems (streaming, async jobs, state, caching, evaluation)
• Strong Python (ideally .NET, C# as well) backend development skills, with experience building APIs and services, and comfort contributing to front‑end applications
• A solid understanding of software development principles, including design patterns, data structures, and algorithms
• Experience using AI tools (such as Claude Code, Cursor, Codex) and interest in leveraging them to improve engineering efficiency
• Strong communication skills, with the ability to explain complex technical concepts clearly to both technical and non‑technical audiences
• A strong appreciation of Kubernetes, Infrastructure as Code, GitOps, CI/CD practices, and cloud infrastructure (AWS or GCP)
• Comfort working in a fast‑paced, sometimes ambiguous start‑up environment with changing priorities

What we can offer you:

• Competitive salary & annual bonus
• Share options
• Quarterly team socials & annual company offsite
• Hybrid working + 1 month “work from anywhere”
• 25 days holiday + bank holidays
• Take your birthday off
• £750 annual learning & development budget
• Private healthcare (incl. dental & optical)
• Enhanced parental leave
• Additional perks: Cycle to Work, Workplace Nursery salary sacrifice scheme, and top‑quality equipment

Definely is revolutionising how legal professionals access and understand information in complex documents. Our LegalTech solutions integrate directly into legal workflows, enabling teams to draft, review, and interpret contracts more efficiently, without breaking focus. We’re proud to be recognised among the Top 25 in Deloitte’s UK Technology Fast 50 and backed by Revaia, Microsoft, Google, and Octopus Ventures. Trusted by top firms like A&O Shearman, Dentons, Deloitte, and Barclays, we’re building tools that empower legal teams to work smarter and reduce risk. At Definely, you’ll be part of a mission‑driven, collaborative, and ambitious team committed to innovation and growth.