Senior Backend Software Development Engineer (Java/Python)

About the role

WEX Inc. is a leading and growing global provider of payment processing, information management, and fleet card payment solutions. We hire people who share our passion for continuous innovation and client service that is unparalleled in the industry. We are looking for an experienced Senior Backend Software Development Engineer (Java/Python) to join our Platform Modernization group and help deliver highly scalable, reliable, and secure systems. A successful candidate will have a strong technical background in designing and delivering complex software solutions, proven ability to own features end-to-end, and a mindset that emphasizes quality, testing, and continuous improvement. This individual will be a key contributor to team success, mentoring others, influencing engineering practices, and driving technical excellence as we continue to scale our platforms globally. How you'll make an impact: Design, implement, test, and deploy large-scale software systems with a focus on maintainability, scalability, and performance leading by influence. Demonstrates system-level thinking and technical leadership through influence rather than management. Take end-to-end ownership of stories, regularly delivering complex features and suggesting better implementation paths operating as a senior-level individual contributor with minimal guidance. Consistently write thorough unit, integration, and UI tests; drive test-first approaches and coach others on quality practices. Actively contribute to grooming by asking insightful testability and edge-case questions that improve story quality. Conduct thoughtful design and code reviews, providing meaningful feedback on functionality, architecture, and test coverage. Mentor less-experienced engineers, raising the team's technical bar through coaching and sharing best practices and improving code quality, testing, and delivery practices. Participate in system design and architecture discussions, influencing decisions with deep technical insight, contributing actively to design, grooming, and review discussions, shaping both features and engineering culture. Proactively identify opportunities for automation, refactoring, and improvement to enhance developer productivity and system reliability. Contribute to a culture of collaboration, transparency, and continuous learning across distributed teams in the US and Brazil. Experience you'll bring: Advanced English communication skills. Bachelor's degree in Computer Engineering, Electrical Engineering, Computer Information Systems, Management Information Systems, or a related field. Master's degree. Proven senior professional software engineering experience. Proven expertise in one or more modern programming languages such as Java, Python, C#, or C++. Strong knowledge of data structures, algorithms, and system design principles. Experience building distributed systems, microservices, and RESTful APIs. Demonstrated ability to apply a QA mindset: test-first development, edge-case thinking, and driving quality proactively. Comfortable working across the full stack (front-end, back-end, data, cloud). Track record of mentoring peers and improving engineering practices. Ability to operate independently and confidently while collaborating effectively in agile teams. Desired qualifications & experiences: Experience with Cloud Computing platforms (particularly AWS). Hands-on experience with containerization (Docker, Kubernetes) and CI/CD pipelines. Strong technical fundamentals in Linux, networking, and operating systems. Experience with relational and non-relational databases, including schema design and performance tuning. Familiarity with observability tools (logging, metrics, tracing) to ensure system reliability. Bias toward data-driven decision-making and using metrics to guide improvements.