Senior Application Developer

The Senior Application Developer is responsible for ensuring the stability, support, and continuous modernization of critical enterprise applications that underpin core business operations. This role will serve as the primary technical owner of a mission-critical legacy environment built on the Microsoft stack, which includes the .NET Framework, SQL Server, and IIS. The developer will ensure reliable daily operations while helping to transition the system to modern architecture and development practices.

This position requires a hands-on developer comfortable working in complex, undocumented systems who can balance immediate support needs with long-term improvements. The role will collaborate closely with IT leadership, business stakeholders, and external vendors to maintain the current platform while contributing to decisions regarding upgrades, refactoring, or potential replacement with modern or commercial solutions.

This is an onsite role based in our McLean, VA office.

Key Responsibilities

• Serve as the primary technical owner for internally developed web applications built on the Microsoft stack (.NET Framework, SQL Server, IIS).

• Maintain, troubleshoot, and enhance legacy applications to ensure stability and performance for business-critical operations.

• Analyze and reverse-engineer existing systems to understand business logic, database structures, and integrations where documentation is limited.

• Design and implement improvements to application architecture, code structure, and database design to support long-term maintainability.

• Write, refactor, and optimize complex T-SQL queries, stored procedures, and database objects in Microsoft SQL Server.

• Support and manage IIS-hosted applications, including deployment, configuration, and security updates.

• Develop new functionality using C#, .NET, JavaScript, and related technologies.   

• Build RESTful APIs or service layers to enable integration between legacy systems and newer applications.

• Contribute to technical decisions related to system modernization, including upgrades, refactoring, cloud migration, or evaluation of COTS solutions.

• Help establish modern development practices such as source control, automated builds, testing, and deployment processes.

• Collaborate with business stakeholders to understand existing workflows and translate them into technical solutions.

• Document system behavior, architecture, and dependencies to improve long-term supportability.

• Provide technical leadership for the platform while remaining hands-on in development and support.
   

Basic Qualifications

• Bachelor’s degree in Computer Science, Software Engineering, Information Systems, or related field

• 6+ years of experience developing and supporting applications in the Microsoft ecosystem (C#, VB.NET, SQL Server)

• Strong experience working with .NET Framework applications (WebForms, MVC, WCF, or similar)

• Solid experience with Microsoft SQL Server, including writing and debugging complex queries and stored procedures

• Experience supporting applications hosted in IIS environments

• Experience working with existing / legacy ("brownfield") systems

• Experience with HTML, CSS, and JavaScript for web applications

• Strong troubleshooting and problem-solving skills in complex codebases

• Ability to work independently and take ownership of technical solutions

Preferred Qualifications

• Experience modernizing legacy .NET applications to newer versions (.NET 6 / 7 / 8)

• Experience migrating applications to Azure or AWS

• Experience designing APIs or service-based integrations

• Experience with Git, Azure DevOps, or CI/CD pipelines

• Experience evaluating or implementing commercial off-the-shelf (COTS) solutions

• Familiarity with low-code platforms such as Mendix or PowerApps

• Experience in improving or refactoring legacy database schemas

The work environment and requirements described below are representative of those necessary for an employee to successfully perform the essential functions of this role. 

The Physical Side of the Role: Given