Senior Frontend Engineer - Design System London

About the role

As a Senior Software Engineer on our Design System team, you'll be a co-owner of the shared UI foundation that every Synthesia product is built on. You will be shaping direction and making key decisions together with the team, likely with a focus area of your own but context across the whole system. This is a hands‑on engineering role: your primary output is high-quality component code and the tooling around it. The defining challenge of this role is making that foundation AI‑friendly: a design system that both people and AI can build with. As AI tools generate more of our UI, the system has to make it effortless to produce interfaces that are on‑brand, accessible and correct by construction, whether the author is a human or an agent.

You can expect to:

• Build, scale and evolve our design system: the component library, design tokens, and documentation that give product teams a consistent, accessible foundation to build on.
• Extend our design system for AI‑assisted development so AI coding tools and agents can use our components, tokens and guidelines as easily as people can, with Storybook as the backbone and machine‑readable interfaces (e.g. MCP) layered on top.
• Design component APIs that resist misuse, so AI and human developers alike can build with confidence.
• Write high‑quality, performant frontend code (React/TypeScript) and raise the bar for component craft and consistency across the engineering org.
• Partner closely with design, product and engineering to define components together and take them all the way to something that holds up in production.
• Make our components accessible by default, meeting WCAG 2.2 AA, and work closely with our Accessibility engineer to bake in best practices from the start.
• Own the developer experience of the design system: clear documentation, guidelines, Storybook, sensible component APIs, versioning and smooth migration paths that make adoption easy for both human and AI consumers.
• Implement and maintain theming, white labelling, and localization/RTL support so the system works for a global audience.
• Continuously improve the system based on adoption metrics, contributor feedback and new platform capabilities.
• Shape the technical direction of the design system over the next 6–12 months, championing its adoption across teams.

What we're looking for

• At least five (5) years as a software engineer, including three (3) at senior level, building frontend platforms, with real ownership of a design system or shared component library used across multiple products.
• Deep frontend expertise: expert HTML, CSS and JavaScript/TypeScript, with strong React and familiarity with modern build tooling.
• A strong command of component API design, versioning and the developer experience of shared libraries.
• Experience (or strong interest) in making component libraries consumable by AI.
• Solid understanding of responsive design, cross‑browser compatibility and web performance.
• Comfortable building components to WCAG 2.2 AA / EN 301 549 and verifying them yourself with a keyboard and screen reader — accessibility is part of your definition of done, not a separate pass.
• A strong sense of craft and attention to detail, and the ability to balance design intent with engineering constraints.
• Strong communication and collaboration skills, and a passion for improving developer productivity and end‑user experience.

Nice to haves

• A strong design sensibility — an eye for visual detail and the judgement to push back on and improve design decisions, not just build them.
• Experience implementing multi‑brand theming in production.
• Experience with localization and internationalization (including RTL) for a global audience.

Other important info

Our preference is for this role to be based either in‑office or remote in London, UK. We can also accommodate remote workers in other locations across Europe subject to compliance and right‑to‑work checks. The salary starts at EUR/GBP/CHF 120,000 base + stock option plan. This is full‑time employment only, usually through OysterHR. No contractors possible. Everyone at Synthesia gets 25 days of leave + local holidays (no extra paid or unpaid leave possible). We only sponsor VISA if you are in the UK/EU country already and need support.