Principal Software Engineer

SR2 REC LTD; Greater London; On-site; GBP 120,000 - 160,000; Full time

Job summary

A leading tech recruiting firm in Greater London is looking for a Principal Software Engineer to develop backend systems that support AI research. The role requires at least 5 years of experience and a strong focus on software quality. You'll build tools that influence complex model testing and deployment while collaborating with technical stakeholders. This is a high-impact position for engineers who want significant ownership and responsibility in their work.

Benefits

Competitive salary

Benefits package

Qualifications

• At least 5 years of backend engineering experience.
• Experience with complex systems engineering.
• Understanding of AI/ML principles.

Responsibilities

• Build and improve backend systems for internal use.
• Collaborate with stakeholders to solve ambiguous problems.
• Take ownership of software from idea to production.

Skills

Python

FastAPI

System Design

Code Quality

Problem Solving

Job description

Principal Software Engineer | London | £120k to £160k + benefits | Python

This is an exceptional individual contributor role for engineers who want to work on problems that actually matter and be in environment where you're not the smartest person in the room.

You will be building backend systems that support advanced AI research and deployment decisions. The software you work on influences how complex models are tested, understood, and monitored before they reach the real world.

This is serious engineering in a fast moving space, with high expectations around quality, reliability, and judgement.

What you will work on

• Building and improving backend systems used by internal teams every day using FastAPI
• Working on tools that operate at scale and need to be both fast and dependable
• Helping shape how new systems are designed and brought into production
• Collaborating closely with technical stakeholders to solve ambiguous problems
• Taking real ownership over the software you build

Most of the work is Python, but this is not scripting. You will be designing systems that need to be correct, reliable, and maintainable under real load.

What makes this role different

• You are close to the problem, not buried under layers of abstraction
• You work directly with stakeholders, researchers and influence how tools are designed
• You will own features end to end, from idea through to production use
• Engineering standards are high, but speed still matters
• This is a role where judgement counts more than dogma

What they are looking for

• Backend engineers who enjoy complexity and responsibility and have at least 5 years+ experience
• People who care about code quality but know when to move quickly
• Engineers who think in systems, not just features
• Experience with or an interest in LLMs
• Those motivated by the impact of AI and how it is developed

Experience with LLMs, agents, cloud platforms, or security is a bonus, not a requirement.

This is a career defining role for someone who wants to stay deeply technical and work on problems that will only become more important over the next decade.