Senior .NET Developer – Financial Systems & Integrations

Senior • On-site

Rockville, MD

ASSYST is seeking a highly skilled and self-driven Senior Software Developer to support and enhance complex, enterprise-scale financial applications. This role involves working on custom-built systems handling high-volume transactions, including payments, reconciliation, reporting, and multi-system integrations.

The ideal candidate is detail-oriented, capable of working independently, and experienced in solving complex financial and technical challenges.

Key Responsibilities:

Maintain and enhance legacy and custom financial applications
Analyze and modify application logic with minimal documentation
Design and develop scalable software solutions and integrations
Implement API, database, and file-based system integrations
Improve UI/UX with modern, responsive design practices
Troubleshoot and resolve complex financial system issues
Collaborate with technical teams and document solutions

Technical Skills:

HTML, CSS, JavaScript (Bootstrap or Tailwind)
Responsive and mobile-first UI/UX design
C#, ASP.NET (WebForms, MVC, .NET Core)
Azure Entra ID / Azure AD B2C
Microsoft SQL Server
System integration (API, DB, file-based)
Microsoft DevOps & system administration (IIS, networking)
Familiarity with AI-assisted development

Required Experience:

7+ years maintaining legacy applications with limited documentation
7+ years developing Finance-Tech solutions (payments, billing, reconciliation)
5+ years integrating with Tyler Technologies MUNIS or similar ERP systems
3+ years recent experience with Paymentus integrations (iframes, redirects, UAT/production)
7+ years UI/UX development with responsive design (recent experience required)
Proven ability to work independently and deliver practical solutions

ASSYST is an Equal Opportunity Employer. Qualified applicants will receive consideration for employment without regard to race, color, religion, sex, age, disability, military status, national origin or any other characteristic protected under federal, state, or applicable local law.

ASSYST

ASSYST is a technology company specializing in enterprise-scale financial software solutions. Operating within the finance and public-sector technology space, it focuses on developing, maintaining, and modernizing complex, high-volume transaction systems that support payments, billing, reconciliation, reporting, and multi-system integrations. The company demonstrates strong expertise in legacy system enhancement, ERP integrations (including platforms such as Tyler Technologies MUNIS), and secure payment technologies, leveraging Microsoft-based technologies and modern development practices. ASSYST emphasizes technical excellence, problem-solving, and innovation, and is committed to equal opportunity and inclusive employment practices.

Check if your resume is ATS-ready before applying →Build an ATS-optimized resume