Senior Software Engineer

Our Purpose Mastercard powers economies and empowers people in 200+ countries and territories worldwide. Together with our customers, we’re helping build a sustainable economy where everyone can prosper. We support a wide range of digital payments choices, making transactions secure, simple, smart and accessible. Our technology and innovation, partnerships and networks combine to deliver a unique set of products and services that help people, businesses and governments realize their greatest potential. Title and Summary Senior Software Engineer Who is Mastercard? Mastercard is a global technology company in the payments industry. Our mission is to connect and power an inclusive, digital economy that benefits everyone, everywhere by making transactions safe, simple, smart, and accessible. Using secure data and networks, partnerships and passion, our innovations and solutions help individuals, financial institutions, governments, and businesses realize their greatest potential. Our decency quotient, or DQ, drives our culture and everything we do inside and outside of our company. With connections across more than 210 countries and territories, we are building a sustainable world that unlocks priceless possibilities for all. About the Role Join Mastercard’s Transaction Stream team in O’Fallon, MO, and help build the applications and services that power critical capabilities across the real-time payment network. This is an opportunity to work on software that operates at global scale, where speed, reliability, and resilience matter every day. As a Senior Software Engineer, you will collaborate with engineers and product partners to design, build, test, and enhance solutions that support the movement of transactions around the world. Role As a Senior Software Engineer, you will:

• Design, develop, and maintain scalable test frameworks and automation solutions aligned with enterprise architecture standards
• Apply software design principles and architectural patterns to create maintainable and extensible testing and validation systems
• Contribute to system architecture discussions, ensuring solutions are testable, observable, secure, and performant
• Translate business and system requirements into well-designed technical solutions, test strategies, and validation models
• Ensure secure coding practices are embedded in development and testing processes, proactively identifying vulnerabilities and risks
• Develop and execute testing strategies across all levels: unit, functional, integration, system, and performance testing
• Leverage data structures and algorithms to optimize test execution, data handling, and performance validation
• Collaborate in Agile environments, contributing to backlog refinement, sprint planning, and design discussions

Responsibilities Software Engineering & Development

• Design, build, test, deploy, and maintain software components, automation frameworks, and validation tools
• Apply strong knowledge of data structures, algorithms, and efficient coding practices in building scalable solutions
• Contribute to end-to-end software development lifecycle, including design, development, testing, deployment, and monitoring

Architecture & Design

• Participate in defining software architecture and design patterns to ensure scalability, reliability, and maintainability
• Ensure systems are designed for testability, observability, performance, and operational readiness
• Provide input into microservices and cloud migration strategies

Quality Engineering & Testing

• Develop and implement test automation frameworks and CI/CD integration pipelines (e.g., Jenkins, XLR)
• Design comprehensive test strategies and plans, including performance, reliability, and production simulation testing
• Ensure high code quality and coverage using tools such as Sonar or Clover

Security & Compliance

• Apply and promote secure coding practices, including code analysis, vulnerability detection, and mitigation strategies
• Integrate security testing into CI/CD pipelines

Code Quality & Reviews

• Conduct and lead code reviews, ensuring adherence to coding standards, security practices, and maintainability
• Act as a technical reviewer for system designs, test strategies, and implementation approaches

Operability & Performance

• Ensure systems are observable, monitorable, and resilient across environments
• Perform performance engineering, including load testing, tuning, and bottleneck analysis
• Troubleshoot complex production issues and ensure rapid resolution

Collaboration & Leadership

• Partner with developers, architects, and product teams to drive engineering best practices
• Mentor junior engineers and contribute to knowledge sharing across teams
• Evaluate and recommend tools, technologies, and frameworks for continuous improvement

All About You

• Experience building applications and REST APIs using Java, Spring Boot, and Spring Data JPA
• Strong foundation in computer science fundamentals, including data structures, algorithms, and object-oriented design
• Ability to write clean, secure, testable code and contribute to unit, service, and integration testing.
• Comfort working with SQL and relational data concepts.
• Strong analytical and problem-solving skills, with the ability to debug issues and identify practical solutions.
• Strong verbal and written communication skills and the ability to work effectively in a collaborative team environment.
• Self-motivated, organized, and eager to learn, with a passion for continuous improvement and delivering results.
• Strong hands-on experience in software engineering, including development and quality engineering

• Proven experience working with:

• Testing across platforms: Linux and web applications
• Automation development and CI/CD integration and deployment (Jenkins / XLR) and code coverage tools (Sonar, Clover) to ensure high code/ conditional coverage
• Unit, functional, and integration testing
• Performance testing and engineering

• Strong knowledge and understanding of:

• Software design principles (OOP, modularity, design patterns)
• Software architecture concepts (microservices, distributed systems, scalability)
• Data structures and algorithms
• Experience with secure coding practices and application security principles (e.g., OWASP)
• Ability to contribute to system design and architecture decisions

Preferred Qualifications

• Experience in cloud and microservices architecture or mainframe modernization
• Experience designing systems for reliability, performance, and scalability
• Domain knowledge in payments and transaction processing systems
• Bachelor’s or master's degree in computer science or equivalent experience is preferred

Mastercard is a merit-based, inclusive, equal opportunity employer that considers applicants without regard to gender, gender identity, sexual orientation, race, ethnicity, disabled or veteran status, or any other characteristic protected by law. We hire the most qualified candidate for the role. In the US or Canada, if you require accommodations or assistance to complete the online application process or during the recruitment process, please contact View email address on click.appcast.io and identify the type of accommodation or assistance you are requesting. Do not include any medical or health information in this email. The Reasonable Accommodations team will respond to your email promptly. Corporate Security Responsibility All activities involving access to Mastercard assets, information, and networks comes with an inherent risk to the organization and, therefore, it is expected that every person working for, or on behalf of, Mastercard is responsible for information security and must: Abide by Mastercard’s security policies and practices; Ensure the confidentiality and integrity of the information being accessed; Report any suspected information security violation or breach, and Complete all periodic mandatory security trainings in accordance with Mastercard’s guidelines. In line with Mastercard’s total compensation philosophy and assuming that the job will be performed in the US, the successful candidate will be offered a competitive base salary and may be eligible for an annual bonus or commissions depending on the role. The base salary offered may vary depending on multiple factors, including but not limited to location, job-related knowledge, skills, and experience. Mastercard benefits for full time (and certain part time) employees generally include: insurance (including medical, prescription drug, dental, vision, disability, life insurance); flexible spending account and health savings account; paid leaves (including 16 weeks of new parent leave and up to 20 days of bereavement leave); 80 hours of Paid Sick and Safe Time, 25 days of vacation time and 5 personal days, pro-rated based on date of hire; 10 annual paid U.S. observed holidays; 401k with a best-in-class company match; deferred compensation for eligible roles; fitness reimbursement or on-site fitness facilities; eligibility for tuition reimbursement; and many more. Mastercard benefits for interns generally include: 56 hours of Paid Sick and Safe Time; jury duty leave; and on-site fitness facilities in some locations. THIS POSTING RELECTS ONE OR MORE CURRENT VACANCIES ON OUR TEAM, AND MASTERCARD INTENDS TO FILL THIS POSITION BY 10/14/2026. If the fill date has passed, Mastercard intends to fill this position as soon as possible. Pay Ranges O'Fallon, Missouri: $115,000 - $184,000 USD MasterCard