Senior Software Engineer Startup Jobs in Missouri

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
Overview
Mastercard's Network & Digital Payments group creates meaningful digital payment experiences for consumers, merchants, issuers, and partners at global scale.
The Global Product Engineering team builds foundational payment solutions that are secure, resilient, scalable, and operationally reliable. This role is for a Senior Software Engineer who will contribute to the design, development, validation, automation, and operability of high-quality software solutions.
The ideal candidate brings strong software engineering fundamentals, hands-on Java development experience, and a quality-first mindset, with the ability to build automation frameworks, contribute to application design, improve engineering practices, and support production readiness.
Role
As a Senior Software Engineer, you will independently execute key elements of software engineering projects and processes by applying strong technical knowledge, engineering best practices, and problem-solving skills.
You will contribute to building and maintaining scalable software solutions, with a focus on testability, automation, performance, security, resiliency, and operational excellence.
Key Responsibilities
• Design, develop, and maintain high-quality software components, automation frameworks, and engineering tools that improve software delivery confidence.
• Build and enhance automated solutions for unit, functional, integration, API, UI, regression, and end-to-end validation.
• Contribute to software design and architecture discussions with a focus on scalability, testability, reliability, performance, security, and maintainability.
• Develop robust test automation using Java, Spring, JUnit, Rest Assured, JBehave, Cucumber, or similar frameworks.
• Participate in code reviews and provide actionable feedback to improve code quality, security, maintainability, and adherence to engineering standards.
• Collaborate with software engineers, architects, DevOps engineers, product owners, and program teams to understand requirements and deliver business-aligned solutions.
• Create and maintain technical artifacts such as design notes, test strategies, automation plans, integration specifications, and operational readiness documentation.
• Support CI/CD adoption by integrating automated checks into Jenkins, Bamboo, Git-based workflows, code coverage tools, and static analysis platforms.
• Identify gaps across unit, functional, integration, regression, performance, and exploratory validation, and work with engineering teams to address them.
• Contribute to performance engineering by identifying bottlenecks, validating system behavior under load, and supporting tuning efforts.
• Apply secure coding practices and support vulnerability identification using tools such as Sonar, Checkmarx, Fortify, or similar platforms.
• Support production readiness through logging, monitoring, troubleshooting, incident analysis, root cause analysis, and problem resolution.
• Participate in defect triage, release readiness reviews, environment validation, and risk assessment across delivery cycles.
• Evaluate emerging tools, frameworks, and engineering practices; support Proof of Concept efforts and continuous improvement initiatives.
• Contribute to solution and technology roadmaps by providing inputs on automation, quality engineering, observability, performance, and operability improvements.
• Work in an Agile environment, actively participating in sprint planning, daily stand-ups, demos, retrospectives, and release planning.
All About You
The ideal candidate will have hands-on software engineering experience with strong technical depth across development, automation, testing, and delivery practices.
Required Skills and Experience
• 6-9 years of software engineering experience with strong hands-on Java development skills.
• Strong understanding of software development lifecycle, software design principles, data structures, and object-oriented programming.
• Experience designing and developing automation frameworks, reusable test utilities, test harnesses, and engineering productivity tools.
• Hands-on experience with Java, Spring, JUnit, Rest Assured, JBehave, Cucumber, or similar frameworks.
• Strong experience validating APIs, microservices, web services, web applications, databases, and integration flows.
• Good understanding of unit testing, functional testing, integration testing, regression testing, exploratory testing, and acceptance testing.
• Experience integrating automated checks into CI/CD pipelines using Jenkins, Bamboo, Git, Maven, or similar tools.
• Familiarity with code quality, code coverage, and vulnerability scanning tools such as Sonar, Clover, Checkmarx, Fortify, or similar platforms.
• Good understanding of secure coding practices, code review practices, and engineering quality standards.
• Working knowledge of performance engineering concepts, including load testing, bottleneck identification, and system behavior analysis.
• Experience with Linux/Unix environments, shell commands, logs, troubleshooting, and environment validation.
• Strong understanding of REST/SOAP APIs, databases, service integrations, and distributed application behavior.
• Ability to troubleshoot complex technical issues across application, integration, environment, and data layers.
• Strong communication, collaboration, and documentation skills.
• Ability to work independently, manage ambiguity, and deliver under pressure in a fast-paced Agile environment.
• Passion for engineering excellence, continuous improvement, automation, and building reliable software at scale.
Preferred Skills
• Experience with cloud-native applications, containers, Kubernetes, or platform engineering concepts.
• Experience with observability tools such as Splunk, Dynatrace, Grafana, Prometheus, or similar platforms.
• Experience supporting production systems through incident management, root cause analysis, and operational readiness reviews.
• Exposure to payment systems, digital payments, authentication, security, or financial technology platforms.
• Experience contributing to engineering standards, reusable frameworks, shared libraries, or developer productivity platforms.
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 reasonable_accommodation@mastercard.com 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.
Pay Ranges
O'Fallon, Missouri: $115,000 - $184,000 USD