Lead Software Engineer

Mastercard•O'fallon, MO

2d•$140,000 - $231,000•Hybrid

About The Position

Mastercard's Global Credit Authorization team is seeking a Lead Software Engineer to design, build, and validate mission-critical, highly available systems that process secure financial transactions at global scale. The role combines hands-on software engineering with quality engineering to define and execute validation strategies spanning functional behavior, transaction integrity, resiliency, performance, failover, recovery, monitoring, and production readiness. The engineer will develop software and automation using Java and/or Python, maintain representative test environments, and validate complex distributed systems under realistic traffic and failure conditions. The Lead Software Engineer will collaborate with software engineers, architects, operations teams, product owners, and other stakeholders to troubleshoot software and networking issues, analyze defects, and ensure changes meet quality, reliability, performance, and operational-readiness standards before production deployment. The position is based in O'Fallon, Missouri, and requires three days per week onsite.

Requirements

Previous experience as a Senior or Lead Software Engineer, Software Developer, or Software Development Engineer in Test (SDET) working on complex enterprise systems.
Strong hands-on software development experience designing, developing, debugging, and maintaining production-quality applications, services, utilities, or automation.
Hands-on programming experience with Java and/or Python, including backend services, automation, test utilities, or frameworks.
Experience building, configuring, and troubleshooting test, lab, development, or lower-level environments for distributed applications.
Strong understanding of TCP/IP networking, persistent connections, routing, proxies, load balancers, DNS, ports, and network troubleshooting.
Experience analyzing packet captures, logs, traces, metrics, and operational telemetry to troubleshoot complex software and network issues.
Strong experience with functional, integration, resiliency, performance, and end-to-end testing of distributed or highly available systems.
Strong understanding of transaction-processing systems and validation of business-critical workflows and transaction integrity.
Proven experience with failover, recovery, disaster recovery, and business continuity testing for mission-critical systems.
Hands-on experience developing and using automated test frameworks, failure-injection methodologies, and performance testing tools.
Experience with load, stress, soak, scalability, and capacity testing for high-throughput applications and services.
Strong understanding of software engineering and quality practices, including test planning, certification, production readiness, and defect lifecycle management.
Demonstrated ability to perform root-cause analysis across software, infrastructure, and network layers and drive complex technical issues to resolution.
Strong analytical, problem-solving, technical documentation, and communication skills, with the ability to collaborate and influence across engineering, architecture, product, and operations teams.
Bachelor's degree in Computer Science, Software Engineering, Information Technology, Engineering, Mathematics, or a related field, or equivalent practical experience.

Nice To Haves

Experience with financial messaging platforms, ISO 8583, payment switching systems, telecommunications platforms, or other high-availability transaction-processing environments.
Experience testing proxy, load-balancer, network-service, or active-active failover architectures.
Familiarity with large-scale distributed systems requiring stringent availability, resiliency, and performance requirements.
Experience supporting production certification and readiness activities for customer-facing transaction platforms.
Knowledge of observability, monitoring, and operational health validation practices for enterprise-scale services.

Responsibilities

Design, develop, and enhance software, test applications, utilities, and automation solutions using Java and/or Python to support system validation and engineering objectives.
Define and execute validation strategies covering functional behavior, transaction integrity, performance, resiliency, failover, recovery, monitoring, and production readiness.
Build, configure, maintain, and troubleshoot lab and lower-level test environments that replicate production architecture, network configurations, traffic patterns, and system dependencies.
Use knowledge of TCP/IP, persistent TCP connections, proxies, load balancers, routing, and network services to validate application and infrastructure behavior.
Develop and execute end-to-end functional, integration, regression, negative, failover, recovery, load, soak, and capacity testing for highly available distributed systems.
Design and implement automated testing frameworks and tools to improve quality, test coverage, repeatability, and engineering efficiency.
Validate traffic movement, transaction integrity, proxy bypass, rollback, and recovery procedures during maintenance, infrastructure changes, deployments, and failure scenarios.
Reproduce and troubleshoot complex issues by analyzing application code, logs, traces, metrics, network traffic, and packet captures; partner with engineering teams on root-cause analysis and resolution.
Evaluate system performance, scalability, resiliency, capacity, and operational readiness under production-like workloads and failure conditions.
Define acceptance criteria, test evidence, certification documentation, validation reports, and production-readiness recommendations.
Collaborate with software engineers, architects, product owners, and operational teams during requirements analysis, design reviews, Agile ceremonies, testing, certification, and deployment.
Champion software engineering, quality, automation, and continuous-improvement practices, identifying opportunities to strengthen tooling, environments, processes, and system reliability.

Benefits

Insurance, including medical, prescription drug, dental, vision, disability, and 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, prorated based on date of hire.
10 annual paid U.S. observed holidays.
401(k) with a company match.
Deferred compensation for eligible roles.
Fitness reimbursement or on-site fitness facilities.
Eligibility for tuition reimbursement.