Backend Software Engineer

Location: UK, remote with occasional travel

In the words of one of our senior clients recently…

“Market Research has changed more in the past 3 years, than in the previous 40”

About System1.

System1 is The Creative Effectiveness Platform. Our target customers are the world’s largest advertisers. We predict and improve marketing effectiveness. Our advertising and idea tests measure emotion to give our customers the most accurate predictions of the business impact of creativity.

To learn more about us, please visit System1 Group | Create with Confidence

About The Role

We are looking for a talented and ambitious Backend Software Engineer to join the empowered product team building System1’s next-generation AI platform. You will help shape how the world’s largest brands predict and improve the effectiveness of their advertising, building the Python services, APIs and integrations that power the platform. You will work as a first-class member of the product team alongside your Product Manager, Product Designer and Team Lead to discover and deliver outcomes that matter to our customers and our business. This is a rare opportunity to help build a new platform from the ground up, engineer in a genuinely AI-native way, and work at the speed our market demands.

Are you energised by being a true partner in the product team, helping decide what to build, not just how to build it?

Do you already engineer through Claude Code every day, with your own skills and subagents, and the discipline to own every line you ship?

Are you motivated by outcomes over outputs, and by getting production systems working at scale rather than shipping features for their own sake?

Do you want to join us to excite and change the industry?

What will you be doing?

Partner as a member of an empowered product team (Product Manager, Product Designer, Team Lead and engineers), sharing accountability for the outcomes your team commits to.

Contribute to continuous product discovery, helping the team assess feasibility early and building quick technical prototypes to test ideas before we commit to building.

Design, build and own Python backend services for our AI platform, from media upload through asynchronous ML processing to insight delivery.

Work API-first and spec-driven, defining clean REST contracts that serve headless frontends, internal teams and customer integrations.

Build MCP servers that make System1’s data and capabilities available to AI agents and tools, for customers and colleagues alike.

Engineer through Claude Code day to day, building and sharing skills, subagents and workflows that raise the speed and quality of the whole team.

Take code into production at scale with confidence, bringing the testing, observability and reliability our enterprise customers expect.

Contribute to our infrastructure as code and cloud environment, understanding how your services are deployed, run and scaled.

Work alongside our data scientists to bring models into production, learning the machine learning side of the platform as you go.

Build with enterprise security and compliance in mind, so the world’s largest advertisers can trust the platform with their data.

You need to be this kind of person

• A missionary, not a mercenary. You care deeply about the customer problem and the outcome, not just the code.
• Outcome-driven. You measure your success by the change you create for customers and the business, not by tickets closed.
• An engineer first, with AI as a force multiplier. You use AI tools to move faster with rigour, not to skip the thinking.
• Comfortable with ambiguity and ownership. You don’t wait for a perfectly specified ticket, you frame the problem with your team and go.
• A clear communicator, able to explain technical trade-offs to product, design, data science and commercial colleagues as well as to fellow engineers.
• Curious and a lifelong learner, with the integrity to back your point of view with evidence in front of colleagues, customers and stakeholders.
• Able to see the bigger picture without losing attention to detail, your code quality is as strong as your product thinking.
• A natural collaborator, comfortable working with all departments at all seniorities, and equally able to drive work forward independently.
• Passionate about (good!) advertising, how it works and how it can be improved or excited to become so.

You need to have the following experience

• To be successful in this role, you will have approximately 3–5 years of real-world software engineering experience and be ready to operate as a first-class member of an empowered product team, where you’ll have outsized influence on the outcomes we deliver.
• Strong commercial experience building backend services in Python.
• Experience designing and building REST APIs, ideally spec-driven, with a clear understanding of what frontends need from a headless architecture.
• Experience building SaaS software and taking code into production at scale, whether as part of a team or with personal responsibility for it.
• Hands-on experience with at least one major cloud platform (e.g. AWS, Azure, GCP).
• A working understanding of infrastructure as code and the ability to contribute to it.
• Solid experience working with databases and data modelling.
• Daily use of Claude Code as an engineering tool, including building your own skills and subagents, with an engineering-led approach rather than vibe coding.
• Experience building MCP servers, or a strong understanding of MCP and a drive to build with it.
• Experience working in a product operating model, as part of an empowered, cross-functional product team.
• Familiarity with the security and compliance requirements of enterprise customers.
• Familiarity with machine learning systems, or a genuine desire to learn, is a plus.
• This role will require you to operate across multiple discovery and delivery threads in parallel, balancing speed with the rigour and reliability our customers expect.

Benefits

We offer a competitive salary and bonus scheme, including health insurance, and pension. Our people are important to us, and we understand that each person has a life outside of work and we therefore offer flexible, remote working within the UK, with occasional travel to get together for company and team meet-ups. We also offer several wellbeing resources such as “de-clutter” afternoons for your personal and professional needs.

We encourage learning and offer education reimbursement opportunities.

We have recognition schemes, and regular socials, including summer and winter parties!

We welcome applicants from all diverse communities and encourage our candidates to ask us about reasonable adjustments that we may be able to make to support through our recruitment process and while in post.