Senior Staff Backend Engineer / Technical Lead – AI-Native Infrastructure Startup – London – Ex[...]

My client, a high-growth London-based AI startup, is seeking a Senior Staff Backend Engineer / Technical Lead to join their senior engineering team.

This is a rare opportunity to join an ambitious, engineering-led business at a pivotal stage of growth. The company is building complex, business-critical communications and AI-driven infrastructure, and is looking for a highly experienced backend engineer who can combine deep technical expertise with leadership, ownership, and strong execution.

They operate as an AI-native engineering organisation - not as a buzzword, but in how they actually build. AI tooling, LLM-powered systems, and rapid iteration are embedded into daily workflows. The team is small, highly capable, and ships fast - with real user impact from day one.

The ideal profile is someone operating at the level of a Meta E6 / Staff Engineer equivalent, with a background in large-scale backend systems, technical leadership, and experience working on high-performance distributed systems.

This role is designed for a senior individual contributor who can act as a key technical partner to leadership, drive critical architectural decisions, and play a central role in scaling core infrastructure in a fast-moving startup environment.

You will join a small, highly capable team and work directly alongside the CTO and Founder (ex-JP Morgan) and Head of Engineering (ex-Meta), partnering on some of the company’s most important technical challenges. This is a high-ownership environment where engineers are trusted to lead from the front, solve difficult problems, and have real influence over systems, architecture, and technical direction from day one.

A successful candidate will be a highly capable senior backend engineer with strong leadership presence, excellent technical depth, and a genuine desire to build in a startup environment. You will be someone who can operate with autonomy, move quickly, and make sound decisions under ambiguity.

Requirements:

• 5+ years of professional software engineering experience, with deep expertise in backend and distributed systems.
• Experience operating at Staff / Senior Staff / Principal Engineer level, or equivalent.
• Strong backend engineering skills, ideally in high-scale or business-critical infrastructure environments.
• Proven experience leading major technical initiatives and driving cross-team outcomes.
• Strong understanding of system design, distributed systems, reliability, and performance optimisation.
• Exposure to messaging systems, communications infrastructure, real-time systems, or similar domains is highly desirable.
• Experience with high-performance or less common backend technologies (e.g. Elixir, Erlang, Rust, Go) is a strong plus, but not required.
• A hands-on builder mindset with the ability to combine execution and technical leadership.
• Prior startup experience is a plus.
• Based in London or willing to relocate for an in-person role.

Tech Environment:

• Backend and infrastructure-focused systems with high performance and reliability requirements.
• Modern stack including TypeScript, Node.js, and distributed systems tooling.
• AI-native workflows with LLM-powered systems and internal AI tooling embedded into development.
• Infrastructure and data tooling including technologies such as SingleStore, OpenSearch, Trigger.dev, and Axiom.

You can expect:

• A high-ownership, small-team environment where your work has immediate and visible impact on core systems.
• Direct collaboration with the CTO and Head of Engineering on critical technical and architectural decisions.
• Equity in a fast-growing startup with significant upside potential.
• An engineering-first culture focused on clean code, strong systems thinking, and rapid iteration.
• An AI-native environment where modern tools and workflows are embedded in daily engineering work.
• The opportunity to operate with high autonomy and influence both technical direction and team outcomes.
• A centrally located office in Marylebone.
• Membership to a premium/luxury gym.
• Visa sponsorship available for the right candidate.
• Preference for Spanish-speaking candidates (not essential).

This role is ideal for a senior backend engineer or technical leader looking to step into a high-impact position, work closely with leadership, and help build the core infrastructure of a rapidly scaling AI business.

To apply, please submit your CV or contact gala.santaballa@mondrian-alpha.com directly.

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