Staff Software Engineer, Square Cards

Since we opened our doors in 2009, the world of commerce has evolved immensely, and so has Square. After enabling anyone to take payments and never miss a sale, we saw sellers stymied by disparate, outmoded products and tools that wouldn't work together.

So we expanded into software and started building integrated, omnichannel solutions – to help sellers sell online, manage inventory, offer buy now, pay later functionality, book appointments, engage loyal buyers, and hire and pay staff. Across it all, we've embedded financial services tools at the point of sale, so merchants can access a business loan and manage their cash flow in one place. Afterpay furthers our goal to provide omnichannel tools that unlock meaningful value and growth, enabling sellers to capture the next generation shopper, increase order sizes, and compete at a larger scale.

Today, we are a partner to sellers of all sizes – large, enterprise-scale businesses with complex operations, sellers just starting, as well as merchants who began selling with Square and have grown larger over time. As our sellers grow, so do our solutions. There is a massive opportunity in front of us. We're building a significant, meaningful, and lasting business, and we are helping sellers worldwide do the same.

The Role

Square empowers small businesses to thrive, and the Square Debit Card is at the heart of that mission. Sellers use it every day to pay vendors, cover payroll, and reinvest in their growth—knowing they can access their money instantly. The Cards team builds the systems and experiences that make this possible: activation experiences that feel effortless, digital wallet integrations that feel seamless, rewards that build loyalty, and resilient platforms that sellers trust with their livelihoods.

As a Staff Software Engineer, you'll help define the future of how sellers access and spend their money. You'll take on some of the hardest engineering problems in fintech—balancing scale, iteration, and simplicity—while shaping systems that other teams across Square and Cash will rely on. This is a hands-on role with org-wide impact: you'll write code, set technical direction, and mentor senior engineers, all in service of building financial tools that millions of businesses depend on every day.

You Will

• Define the technical vision for seller-facing card systems, from activation and onboarding to incentives and account management, ensuring they scale across geo markets and teams.
• Drive integrations that make Square Cards effortless to use across digital wallets, third-party platforms, and card-on-file experiences throughout the Square ecosystem.
• Architect resilient frameworks with robust fallback and failover paths, setting standards for reliability across Banking.
• Build shared infrastructure for incentives and rewards, enabling product teams to experiment and deliver long-term seller engagement at scale.
• Mentor senior engineers, shaping design practices, and codifying standards for reliability, security, and scalability.
• Partner with product, design, ML, risk, and compliance leaders to deliver trusted financial experiences that advance Square's mission globally.

You Have

• 12+ years experience building and scaling large, distributed systems.
• A track record of setting technical direction and delivering impact across multiple teams.
• Expertise in backend engineering (Java, Kotlin, or similar), with the ability to quickly learn new stacks.
• Experience designing frameworks and platforms that others rely on.
• A history of mentoring senior engineers and raising the technical bar for entire teams.
• Strong communication skills and the ability to align technical decisions with business priorities.
• A drive to build resilient, trustworthy systems in high-stakes domains like payments or fintech.
• A mindset that balances fast iteration with building for the long term.

Technologies We Use and Teach

• Backend: Java, Kotlin
• Data: MySQL, DynamoDB, Kafka, SQS
• Infra: Kubernetes, AWS, Terraform, Protocol Buffers, Temporal
• Clients: TypeScript, React Native, Swift, Kotlin

We're working to build a more inclusive economy where our customers have equal access to opportunity, and we strive to live by these same values in building our workplace. Block is an equal opportunity employer evaluating all employees and job applicants without re