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Freelance Mainframe Applications Developer Jobs in Washington

Senior .NET Developer (Onsite)

Columbia, MD · On-site

$53.75 - $70.75/hr

NET Developer to support large-scale enterprise modernization initiatives focused on transforming legacy Mainframe applications into modern, cloud-ready .NET platforms. * The ideal candidate will ...

Mainframe SRE

Upper Marlboro, MD · On-site

$48.50 - $62.50/hr

Operate, monitor, and maintain IBM z/OS mainframe environments supporting mission-critical government applications * Implement Site Reliability Engineering (SRE) principles including SLOs, error ...

Senior Mainframe Engineer Location: remote Pay rate: open to W2 and established 1099s Position type ... Experience with FIS/Systematics core banking applications is highly preferred. The role also ...

We are always looking for talented people to join Miltton. If you are interested please send us your information in English, Finnish or Swedish. Locations Miltton USA, Miltton New Nordics, Miltton ...

... critical mainframe systems and applications, including CICS, Db2, IMS, JES, MQ, and related ... Advanced REXX programming experience within enterprise mainframe environments. * Strong hands-on ...

... critical mainframe systems and applications, including CICS, Db2, IMS, JES, MQ, and related ... Advanced REXX programming experience within enterprise mainframe environments. * Strong hands-on ...

New

... critical mainframe systems and applications, including CICS, Db2, IMS, JES, MQ, and related ... Advanced REXX programming experience within enterprise mainframe environments. * Strong hands-on ...

Provides Tier 2 desktop support to users for PC, server, mainframe applications, and hardware ... May interact with network services, software systems engineering, and/or applications development ...

... engineering and systems integration. Our tightly integrated offerings are tailored to each clients ... Combining applications, platforms, infrastructure, knowledge processes, and domain expertise allows ...

Responsibilities Peraton is seeking a Mid-Level Software Test Engineer to join our team of ... Experience with IBM Mainframe or Unisys Mainframe applications and operations * Market knowledge of ...

Showing results 21-40

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Infographic showing various Freelance Mainframe Applications Developer job openings in Washington as of August 2026, with employment types broken down into 49% Full Time, 3% Part Time, 5% Temporary, and 43% Contract. Highlights an 80% In-person, and 20% Remote job distribution.

Senior .NET Developer (Onsite)

Serigor, Inc.

Columbia, MD • On-site

$53.75 - $70.75/hr

Full-time

This job post has expired today. Applications are no longer accepted.


Job description

Job Title: Senior .NET Developer (Onsite)
Location: Columbia, MD
Job Type: Full-Time
Job Description:
  • We are seeking a highly experienced Senior .NET Developer to support large-scale enterprise modernization initiatives focused on transforming legacy Mainframe applications into modern, cloud-ready .NET platforms.
  • The ideal candidate will have strong expertise in enterprise Microsoft technologies, distributed systems, APIs, database modernization, DevOps, and cloud platforms. This role involves working closely with modernization teams to support application conversion, remediation, integration, testing, and cloud enablement efforts.
  • Experience supporting Mainframe modernization, automated code conversion, and enterprise transformation programs is highly preferred.

Key Responsibilities:
  • Design, develop, enhance, and support enterprise-grade applications using modern .NET technologies
  • Support Mainframe-to-.NET modernization and migration initiatives, including AI-assisted code conversion efforts
  • Refactor and optimize converted code to align with modern .NET engineering standards and architecture principles
  • Develop RESTful APIs, gRPC services, backend services, batch jobs, and distributed integration solutions
  • Build scalable, maintainable, and high-performance applications
  • Support enterprise database modernization, data migration, DB2 integration, and SQL Server optimization
  • Collaborate with Mainframe SMEs, architects, QA teams, DevOps engineers, and business analysts
  • Support remediation, integration testing, regression testing, and functional equivalence validation
  • Contribute to CI/CD pipelines, DevOps automation, deployment processes, and modernization frameworks
  • Troubleshoot application issues, perform root cause analysis, debugging, and performance tuning
  • Work within AWS and Azure cloud environments
  • Develop technical documentation, deployment guides, and operational runbooks
  • Mentor junior developers and contribute to engineering best practices

Required Qualifications:
  • 10+ years of enterprise .NET development experience
  • Strong hands-on expertise with:
    • C#
    • ASP.NET / ASP.NET Core
    • .NET Framework / .NET Core / .NET 6+
    • Web APIs / RESTful Services
    • gRPC Services
    • Entity Framework / EF Core
    • Angular and/or React
    • JavaScript
    • LINQ
    • Windows Services and scheduled batch processing
    • PowerShell scripting
  • Strong experience building distributed and service-oriented applications
  • Solid understanding of:
    • Object-Oriented Programming (OOP)
    • SOLID principles
    • Design patterns
    • Secure coding practices
  • Experience with:
    • Microservices architecture
    • API integrations
    • Git and Azure DevOps
    • CI/CD pipelines and DevOps automation
    • Docker and containerization
    • Kubernetes or container orchestration platforms
  • Strong database expertise with:
    • Microsoft SQL Server
    • DB2
    • Stored procedures
    • Query optimization
    • Data migration and performance tuning
  • Experience with messaging/event technologies such as Kafka, RabbitMQ, or Azure Service Bus
  • Strong troubleshooting, debugging, and optimization skills
  • Experience working in Agile/Scrum environments
  • Excellent written and verbal communication skills

Cloud & Infrastructure Experience
AWS Experience with:
  • EC2
  • S3
  • IAM
  • CloudWatch
  • Cloud-based deployments and monitoring
  • Hybrid cloud environments

Microsoft Infrastructure Experience with:
  • Windows Server
  • IIS deployment and configuration
  • Enterprise application hosting and deployment support

Preferred Qualifications:
  • Experience supporting Mainframe modernization initiatives involving:
    • COBOL-to-.NET transformation
    • AI-assisted code conversion
    • Functional equivalence validation
    • Legacy application modernization
  • Exposure to Mainframe technologies such as:
    • COBOL
    • JCL
    • CICS
    • VSAM
    • DB2
    • IMS
  • Experience supporting government, financial, healthcare, tax, or other large enterprise modernization programs
  • Experience with automated modernization tools and modernization factory delivery models
  • Exposure to hybrid and multi-cloud enterprise environments