UI Engineer II

Mollie; Lisboa; On-site; EUR 60,000 - 90,000; Full time

Job summary

Mollie in Lisbon is seeking a UI Engineer to bridge frontend, backend and infrastructure, owning the design system and navigation experience used by merchants.

You will work across App Core and App Engagement, accelerating releases, building reusable patterns, improving accessibility, testing and automation, and driving product activation at scale.

This role offers impact across Europe in a hands-on, collaborative culture with a strong maker ethos.

Responsibilities

• Scale the mobile app architecture to support growing user demand.
• Improve and own the release process, moving from bi-weekly to weekly deployments.
• Build reusable patterns, tooling, and documentation for engineers across domains.
• Support debugging and feature delivery for teams across Mollie as a platform partner.
• Own and evolve the Mollie UI design system, ensuring consistency across web and mobile.
• Rebuild and improve the mobile navigation architecture, covering system design and visuals.
• Improve app accessibility in line with compliance standards.
• Strengthen testing practices and automation to raise reliability and reduce regressions.
• Own the Upsell infrastructure and in-app messaging for targeted campaigns.

Job description

About the Role

• Creating clean, well-documented APIs, reliable tooling and smooth workflows that make development, testing, localisation, and releases easier and more predictable.
• Owning the design system and navigation experience that merchants interact with every day, driving engagement, accessibility, and product activation at scale.
• 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.
• You will have ownership, visibility, and the chance to do work that matters at scale.

What You'll Be Doing

Depending on which team you join, your work will focus on one of the following areas:

App Core

• Scale the mobile app architecture to support growing user demand, with a focus on quality and long-term maintainability.
• Accelerate the app release cadence by improving and owning the release process, moving from bi-weekly to weekly deployments.
• Build reusable patterns, tooling, and documentation that allow engineers across all domains to contribute to the mobile app without needing deep mobile expertise.
• Support debugging and feature delivery for teams across Mollie, acting as a platform partner to product teams who depend on the AppCore foundations.

App Engagement

• Own and evolve the Mollie UI design system, ensuring consistency and quality across web and mobile.
• Rebuild and improve the mobile navigation architecture, covering both the system design and the visual experience.
• Improve app accessibility in line with compliance standards, making Mollie more inclusive for all merchants.
• Strengthen testing practices and automation to raise reliability and reduce regressions across the app.
• Own the Upsell infrastructure and in-app messaging that enables targeted campaigns to drive merchant engagement and product activation.

About Mollie

• At Mollie, we're on a mission to make payments and money management effortless for every business in Europe.
• We started 20 years ago when we launched a more direct, affordable way for companies to get paid, providing an alternative to the frustrating, overpriced solutions that banks offered at the time.
• Today, we serve more than 250,000 businesses across Europe with an all-in-one solution that simplifies payments and money management.
• We're an 850-strong team of product, finance, support, commerce, and engineering specialists working across Europe - from Lisbon to London.
• Our team is driven by a passion for crafting products that our customers love, combining a strong maker culture with cross-functional teams and fast-paced product cycles to bring ideas to life quickly.