Senior Software Engineer - Fullstack

Fospha is dedicated to building the world's most powerful measurement solution for online retail. For over a decade, we've helped teams make smarter decisions with full-funnel marketing insights, forecasting, and optimisation. With Fospha, every team moves faster and grows smarter.

Trusted by leading brands across three continents, including Gymshark, Huel and Oh Polly, Fospha manages $4 billion in annual ad spend.

We're scaling fast across London, Mumbai, and Austin – and we're now looking for a Senior Software Engineer to join our Team!

The Role

As a Senior Software Engineer, you'll build the products our customers rely on every day to make multi-million dollar media decisions. You'll work across the full stack - from crafting responsive, intuitive frontend experiences through to designing and scaling the backend microservices that power them - and, given the seniority of this role, you'll also help shape system design and infrastructure decisions as we scale.

You'll work alongside engineers, product managers, and AI agents as part of our AI-first operating model, where lean, high-autonomy teams ship fast and learn faster. This is a hands-on engineering role for someone who's comfortable owning a feature end-to-end - from initial design through to production - and who wants to grow their craft in a fast-moving, ambitious environment.

Where you'll focus
• Frontend development using modern JavaScript frameworks (React.js or Next.js)
• Backend development using Python-based microservices
• System design and infrastructure, contributing to architectural decisions as we scale
• End-to-end feature ownership across the stack
• (Nice-to-have) Exposure to Data Science / Data Engineering workflows

Key Responsibilities
• Design, build, and maintain full stack features - from frontend UI/UX through to backend services and APIs in Python.
• Contribute to system design and infrastructure decisions, helping evolve our technical foundations as we scale.
• Get involved across the full Software Development Lifecycle, from initial planning and design through execution, release, and monitoring in production.
• Write clean, well-tested, maintainable code, and champion good engineering practices across the team.
• Collaborate closely with product managers, designers, and fellow engineers to translate requirements into working software.
• Build and consume APIs (REST/GraphQL) that connect frontend experiences to backend services.
• Work with AI agents as part of our AI-first operating model, using clear specifications to shape high- quality, AI-assisted engineering work.
• Take ownership of the quality, performance, and reliability of the features you ship.
• Participate in code reviews, giving and receiving candid, constructive feedback.
• Stay curious about new tools and technologies, including opportunities to explore Data Science / Data Engineering problems as they arise.

What are we looking for?

• Have around 5+ years of professional experience as a full stack / senior software engineer, with a balanced skill set across frontend, backend, and infrastructure.
• Have strong, hands-on experience with front-end technologies such as React.js or Next.js, and solid backend experience building and maintaining Python-based microservices.
• Are comfortable contributing to system design and infrastructure decisions, reflecting the seniority of this role.
• Are comfortable working across the full stack and can move fluidly between frontend, backend, and infrastructure concerns.
• Have solid experience working in an agile environment and know how to embed quality into fast-moving teams.
• Bring exceptional attention to detail and a genuine ownership mindset over what you build.
• Are enthusiastic about new technologies, with the ability to adapt and learn quickly - we're open to candidates with strong experience in other modern languages/frameworks if the core skill set and seniority are a strong match.
• Have an awareness of spec-driven AI development and how clear specifications shape the quality of AI- assisted engineering work.
• Have the confidence and initiative to evolve ideas and pull pieces of work together into meaningful change.
• Have an active interest in self-learning and growing your craft.
• Nice-to-have: exposure to Data Science / Data Engineering (not core to the role, but a strong plus).

You don't have to tick every box. If you're a strong engineer who's hungry to step up, we'd still like to hear
from you.

What We Offer
• Competitive salary
• Be part of a leading global venture builder, Blenheim Chalcot, and learn from the incredible talent in BC.
• Be exposed to the right mix of challenges and learning and development opportunities
• Flexible Benefits including Private Medical Subsidiaries, Life Assurance, Pension scheme etc
• 25 days of paid holiday + your birthday off!
• Quarterly team socials

Our Values and Principles - You will be able to demonstrate examples of our core principles:

• Seek inclusion & diversity: We create an environment where everyone feels welcome, and people are encouraged to speak and be heard
• Work Hard, Work Well, Work Together: We take responsibility for making things happen, independently and together; we help colleagues in need and close loops, making sure our work is complete and has lasting impact
• Grow: We are proactive, curious and unafraid of failure
• Customer at the heart: We care about the customer, feel their pain and love building product that solves their biggest problems
• Candour with caring: We deliver candid feedback with kindness and receive it with gratitude

Above all, our people show a willingness to work together and get their hands dirty to deliver product success, which means our customers are successful!