Sr. Principal C#/.NET Engineer (Mission-Critical Systems)

TL;DR

Sr. Principal C#/.NET Engineer (Mission-Critical Systems): Design, implement, and optimize high-performance C# services and frameworks for a large-scale security integration platform with an accent on architectural modernization and complex problem-solving. Focus on refactoring legacy components, troubleshooting multi-threaded distributed systems, and implementing message-based architectures for reliability.

Location: Onsite in Westford, MA (01886), USA

Salary: $164,300–$185,100

Company

Staffing firm providing engineering talent for mission-critical security integration platforms.

What you will do

• Design, implement, and optimize high-performance C# services and frameworks for security ecosystems.
• Lead refactoring and architectural improvements to modernize legacy components.
• Troubleshoot deep bugs, memory issues, and reliability problems in multi-threaded, event-driven systems.
• Implement distributed patterns using message-based architectures, Windows services, sockets, and networking.
• Author technical documentation for APIs, interfaces, and deployment processes.
• Mentor mid-level and senior engineers as a technical authority.

Requirements

• Bachelor’s or Master’s in Computer Science or related field.
• 7–10 years in backend software engineering.
• Expert C# and .NET ecosystem (Framework and Core).
• Strong multi-threaded programming and Windows system-level services.
• Proficiency in networking protocols, sockets, and message-based architectures.
• Experience with Copilot AI and LLM models.
• Ability to work independently in a contract environment with quick ramp-up.

Nice to have

• Experience with security integration or access control platforms.
• Advanced diagnostics: Windows memory dump analysis, profiling, performance tuning.
• SQL Server, ADO.NET, Entity Framework.
• Azure DevOps, GitHub Actions, CI/CD pipelines.

Culture & Benefits

• For temporary assignments 13+ weeks: major medical, dental, vision, 401k, statutory sick pay where required.
• Reasonable accommodations for disabilities.
• Equal opportunity employer; participates in E-Verify.
• Considers qualified applicants regardless of criminal histories per fair chance laws.