Senior Software Engineer - Design Systems

"We may say most aptly that the Analytical Engine weaves algebraic patterns just as the Jacquard loom weaves flowers and leaves." — Ada Lovelace, 1843 What Lovelace saw in the loom was the pattern — flowers and leaves, repeated faithfully, each one begun by a hand that chose it. Mercury is built from patterns too. Every component, every interaction our customers come to trust, starts with someone deciding how it should go, and making it good enough to be used again and again. Tending those patterns, and giving everyone at Mercury the means to weave with them, is the work of our Design System team, and the north star of this role. As a Senior Frontend Engineer on the Design Systems team, you will build and care for those patterns: the components and foundations that everything else at Mercury is built on. Done well, a single decision here makes every product team faster. The ground under that work is shifting, though. Software is being built in new ways, and AI is increasingly part of how design systems are made and used. We are looking for someone who is fluent at that intersection: deeply versed in design systems, and equally as serious about what it takes to build a system that holds up at the leading edge of AI. As part of this role, you will: • Build and maintain the components, patterns, and foundations (tokens, type, color, layout) that Mercury's product is woven from, holding a high bar for accessibility, performance, and pixel-level craft. • Lead projects that ship new UI patterns to solve real pain points for product teams, helping them build better experiences faster. • Develop a design system that's as ready for AI as it is for people, applying the technology to create leveraged outcomes. • Invest in the design system's prototyping experience, shaping the next iteration of how our design function rapidly prototypes, iterates on the product, and explores new concepts. • Raise the craft and AI fluency of the people around you, through mentorship and clear best practices. The ideal candidate for the role: We're looking for someone who cares about the foundational work that lets other people do their best work, and who's eager to help define what a design system means in a world where agents build alongside us. A successful candidate will likely have: • 7+ years of frontend development, with deep experience in React, TypeScript, and modern web technologies. • Experience building or maintaining a design system or shared component library. • A thorough command of modern frontend tooling: build systems, CI/CD, and testing. • High agency, and comfort creating clarity in ambiguous spaces. You take ownership and move without waiting for a defined path. • First-principles systems thinking that stays oriented to outcomes. You make clear decisions that drive toward results instead of getting stuck in open questions. • Strong product taste, and an instinct for leverage: the change that makes many teams better, not the one component polished in isolation. • Hands-on fluency at the intersection of AI and software development: a real command of how emerging AI paradigms are changing the way software gets built, and the ability to turn that into practical leverage, both for the design system itself and for the people who build on it. If this role interests you, we invite you to explore our public demo at demo.mercury.com . *Mercury is a fintech company, not an FDIC-insured bank. Banking services provided through Choice Financial Group and Column N.A., Members FDIC. Mercury values diversity & belonging and is proud to be an Equal Employment Opportunity employer. All individuals seeking employment at Mercury are considered without regard to race, color, religion, national origin, age, sex, marital status, ancestry, ph