Senior/Staff Fullstack Engineer, Avatars in London

Synthesia is the world’s leading AI video platform for business, used by over 90% of the Fortune 100. Founded in 2017, the company is headquartered in London, with offices and teams across Europe and the US. As AI continues to shape the way we live and work, Synthesia develops products to enhance visual communication and enterprise skill development, helping people work better and stay at the center of successful organizations.

About the role

You will work on end-to-end product features across the Avatars and Generative Media domain, building experiences that sit at the core of Synthesia’s product. You will design and deliver features that combine frontend, backend, and AI model capabilities, helping users create and customize avatars, generate content, and interact with generative systems in a reliable and intuitive way.

You will take ownership of features from idea through to production, working with loosely defined requirements to scope, prototype, and ship solutions that deliver real user impact. You will work directly with AI models (both third-party and in-house), evaluating what is possible, understanding reliability constraints, and shaping product decisions based on those capabilities.

You will build across the stack, including:

• Backend systems to support feature logic and model integration
• Frontend experiences that allow users to interact with generative features
• End-to-end workflows that connect user input, model output, and product behavior

You will frequently work on 0 to 1 problems, such as introducing new avatar capabilities or generative features, where experimentation and iteration are critical to success.

You will collaborate closely with product and design to:

• Translate user problems into experiments and features
• Validate what works reliably with underlying models
• Iterate quickly based on feedback and real usage

You will ship features behind feature flags, measure outcomes, and continuously refine based on product and user signals.

What we’re looking for

• You have experience building and shipping full-stack product features end-to-end in production environments.
• You are comfortable working across both frontend and backend, and can independently deliver a feature from concept to implementation.
• You have a strong product mindset and can take ambiguous problems, define scope, and iterate towards solutions that deliver user value.
• You are comfortable working in 0 to 1 environments, experimenting, prototyping, and learning quickly rather than relying on detailed upfront specs.
• You can evaluate technical feasibility and make pragmatic trade-offs, especially when working with imperfect or evolving systems such as AI models.
• You care about reliability and user experience, aiming to build features that work consistently in real-world usage.
• You are confident collaborating with product and design, including pushing back when something is not feasible and proposing better alternatives.
• You are willing to debug and work across the stack, wherever the problem is.
• Experience with AI or ML-powered products, experimentation workflows, or feature flagging is a plus, but not required.

Why join us?

We’re living the golden age of AI. The next decade will yield the next iconic companies, and we dare to say we have what it takes to become one.

Our culture

At Synthesia we’re passionate about building, not talking, planning or politicising. We strive to hire the smartest, kindest and most unrelenting people and let them do their best work without distractions. Our work principles serve as our charter for how we make decisions, give feedback and structure our work to empower everyone to go as fast as possible.

Serving 50,000+ customers (and 50% of the Fortune 500)

We’re trusted by leading brands such as Heineken, Zoom, Xerox, McDonald’s and more.

Proprietary AI technology

Since 2017, we’ve been pioneering advancements in Generative AI. Our AI technology is built in-house, by a team of world-class AI researchers and engineers.

AI Safety, Ethics and Security

AI safety, ethics, and security are fundamental to our mission. While the full scope of Artificial Intelligence's impact on our society is still unfolding, our position is clear: People first. Always.

The hiring process:

• 30-40min call with our Technical Recruiter
• 45min call with an Engineering Manager about your past projects
• 90min Live Coding interview, a collaboration exercise with our Engineer (not Leetcode style)
• 60min System Design, technical discussion usually about a real problem we had in production
• 45min call with leadership, focus on examples of collaboration, growth and going through details of your future team

You can find more details on what to expect and how to prepare HERE. The process does not need to take long - we can be done in seven working days.

Other important info:

• Our preference is for this role to be based either in-office or remote in the following locations: UK, Germany, Switzerland or Ireland.
• We may also be able to support remote workers in other locations across Europe subject to compliance and right to work checks.
• This is full-time employment only - no contractors possible - usually through OysterHR or a local entity.
• Everyone at Synthesia gets 25 days of leave + local holidays.