Principal Engineer (Hiring Immediately) in London

Who are Picnic & what do we do? Picnic’s mission is to drive a higher-quality ad-funded internet. Today, a large proportion of digital advertising is ineffective, intrusive, and poorly optimised. Picnic builds technology that helps brands make better decisions about where and how their advertising is shown - improving outcomes for users, advertisers and publishers. We’re a fast-growing, founder-led startup. Over the last couple of years, we’ve built a strong platform foundation and developed clear conviction around our product direction. We’re now entering a new stage where architectural coherence, reliability and scale matter as much as innovation.

To support this next phase, we’re looking for a Principal Engineer to take ownership of system design, platform evolution and technical quality across the business.

What will you be doing as Principal Engineer? As Principal Engineer, you’ll report to the Chief Product & Technology Officer and act as the technical centre of gravity for Picnic’s systems and architecture - ensuring we build scalable, cost-efficient, production-grade infrastructure as the platform grows. This is a senior individual contributor role first and foremost - focused on building strong systems, raising engineering standards and increasing overall engineering leverage. While this is not primarily a people management position, there is opportunity to take on mentorship and leadership responsibilities within the engineering team. For candidates with the interest and capability, the role can evolve to include greater influence over team development and technical direction as the organisation grows.

You will:

• Act as architectural steward of the platform, ensuring scalability, reliability, performance, and cost efficiency as complexity increases
• Design and evolve backend systems, data pipelines, real-time services, and APIs to support both internal capabilities and external customers
• Introduce clear engineering principles and patterns to reduce duplication and architectural drift across workstreams
• Strengthen AWS architecture and cloud cost efficiency through thoughtful service design, right-sizing, and operational discipline
• Drive best practices around system design, observability, automation, CI/CD, and production operations
• Embed AI-native development workflows across the team - using LLMs and agents effectively for code generation, testing, refactoring, documentation, and experimentation
• Stay close to the systems and codebase, contributing directly to critical components and unblocking complex technical challenges
• Act as a senior technical escalation point, supporting engineers in making strong system-level decisions

Requirements

Who are we looking for? We’re looking for a senior, pragmatic systems engineer - someone who has built and operated complex production systems and enjoys shaping technical direction through code and architecture.

You will:

• Have proven hands-on experience delivering and operating backend or distributed systems in a startup or scale-up environment
• Be deeply experienced in cloud architecture, particularly within AWS
• Have worked across product engineering, infrastructure, and data systems
• Be confident designing systems that balance short-term delivery with long-term maintainability
• Be comfortable integrating AI tools and agent workflows into engineering practice
• Demonstrate strong judgement around trade-offs, technical debt, and operational risk
• Communicate clearly with technical and non-technical stakeholders
• Experience in advertising technology is a bonus!

Benefits

Why work at Picnic? You’ll be joining Picnic at a pivotal moment, where strong architectural decisions and engineering leverage can materially shape the trajectory and value of the business.

At Picnic:

• You’ll have meaningful influence over technical direction without being pulled into heavy people management
• You’ll work closely with the founder and leadership team to translate product strategy into scalable systems
• Ideas move quickly from concept to production - we value momentum, quality and impact
• You’ll help shape an AI-native engineering culture in a small, ambitious team

What can Picnic offer you? We’re proud to have been recognised by Culture100 and Flexa as one of the best and most flexible small businesses to work for. We offer:

• Flexible, hybrid working setup (with regular time in the office throughout the week so you will live in or around London)
• 33 days holiday (inclusive of Bank Holidays)