UI Engineer II

Your opportunity

At Mollie, our mission is to make payments and money management effortless for every business in Europe and the UK. With that mission, the App Core team focuses on enabling product teams to ship customer-facing features faster, across web and mobile, with a great developer experience.

We’re looking for a UI Engineer who’s excited about platform work: improving how features are built, released, and maintained across multiple apps and teams. Rather than owning a single end-user feature, you’ll help create the foundations that allow other teams to move quickly and confidently — from smoother release cycles to better tooling, infrastructure, and localisation workflows.

You’ll work on systems that sit at the heart of our development process, shaping how engineers build, test, release, and scale Mollie’s products. Your work will directly impact hundreds of engineers and, through them, hundreds of thousands of customers.

Join us and be part of a team that's not only shaping the future of payments but also making the right improvements once so teams across Mollie can ship better software, faster.

What you'll be doing

You will be working with us on building and maintaining platform solutions that enable product teams to ship customer-facing features across web and mobile, used by hundreds of thousands of users every month. Our focus is on creating strong foundations that improve how features are developed, released, and operated at scale.

We care deeply about quality and well-designed experiences—not only for our customers, but especially for the engineers building the Mollie's products. This means creating clean, well-documented APIs, reliable tooling and smooth workflows that make development, testing, localisation, and releases easier and more predictable.

As a UI Engineer, you bridge the gap between platform capabilities and the teams that rely on them, working across the frontend, backend and infrastructure as needed.

With multiple releases and deployments happening continuously across web and mobile platforms, code quality, scalability and reliability are critical. Thinking ahead and designing systems that support growth, faster release cycles, and long-term maintainability will be a key part of your work.

Alongside our existing tooling, infrastructure, and release pipelines, we are constantly improving how we modernise our platform, coordinate mobile releases, and support localisation and internationalisation. We’re happy to share more details over a coffee, but it’s safe to say your skills will be challenged — and you’ll have plenty of room to grow and learn quickly.

Our architecture

We come from a monolithic background, with our core systems being written mostly in PHP. As our company started to scale up rapidly, we have scaled our infrastructure along with it by employing services, as well as queueing systems.

Mollie's frontend landscape consists of multiple apps, and each application has its own setup, which is optimised for the app's purpose. Think of our dashboard, API documentation, mobile apps, etc.

In general, our apps are written using TypeScript, in React. Most of our backend systems are written using PHP and are hosted in the Google Cloud.

We work with flexible and reusable components, have an extensive UI library that we maintain internally, and are always looking for parts of the codebase that we can open-source and share with the community.

What you'll bring:

• Always Be Shipping Mindset: It's about consistently delivering value to customers, where speed and quality go hand in hand.

• Minimum of 4 years experience with developing mobile apps & web applications.

• Experience with React & React Native.

• Knowledge of language primitives. You should feel comfortable interacting with native APIs built into the browser.

• While you don't have to be an expert on CSS, you are comfortable implementing a user interface using components available in our design system.

• Experience with test-driven development.

• Experience with creating public or internal REST APIs.

• A knack for creating intuitive and secure user experiences.

• You enjoy being a generalist, working on frontend, backend, as needed to solve problems and delight our users.

Nice to have

• You have experience mentoring other engineers, and like to help others grow in their careers.

• If you have experience with design systems and/or internally developed component libraries, that is a big advantage

Why Mollie?

• Join one of Europe's fastest-growing fintechs and help redefine how businesses manage payments and identity.

• Work from our Lisbon hub with a passionate team of 60+ engineers who love what they do.

• Collaborate across teams and make a direct impact on the scalability of core infrastructure.