The Senior IT Systems Engineer for Corporate Engineering role involves building, integrating, and monitoring internal tooling infrastructure at Brex, focusing on efficient and automated business processes, data-driven decision-making, and integrating internal services, data sources, and SaaS tools. They maintain core systems for authentication, communication, collaboration, and device access, develop SaaS-first solutions for integration and automation, build tools for user self-sufficiency, and provide Tier 3 support as subject matter experts.