Senior Full Stack Developer (.NET Core/React) - 90 % Remote (Poland)

NOTE: This job requires relocation to Poland or that you live within 2 hours radius of Warsaw, the location of the client premises. It is not fully remote, as the client may request for you to come on-site occasionally.

We are looking for an experienced Senior Full Stack .NET Developer / Technical Lead to contribute to the design, development, integration and ongoing support of enterprise-level web applications within a complex IT environment.

The successful candidate will combine strong hands-on development expertise with technical leadership capabilities, ensuring the delivery of scalable, secure and maintainable software solutions.

The role involves working closely with internal stakeholders, development teams and external technology partners, while taking technical ownership of applications throughout their lifecycle, from requirements analysis and solution design through to deployment, maintenance and production support.

Software Development & Architecture

• Design, develop and maintain enterprise web applications using C#, ASP.NET Core / .NET 8, Entity Framework and SQL Server.

• Develop modern, responsive single-page applications using React and TypeScript.

• Translate functional and business requirements into robust technical designs, using UML where appropriate.

• Design and implement application components across the data, business logic and presentation layers.

• Optimize application performance, security, reliability and maintainability.

• Contribute to software integration, prototyping, testing and quality assurance.

Technical Leadership & Delivery

• Provide technical guidance and leadership to development teams, promoting best practices and coding standards.

• Participate in Agile/Scrum development activities, technical planning and effort estimation.

• Conduct code reviews, identify technical debt and propose sustainable improvements.

• Produce and maintain clear technical documentation, solution designs and development specifications.

• Collaborate with external development partners to ensure effective knowledge transfer, application handover and technical continuity.

DevOps, Deployment & Application Security

• Manage application builds, deployments and release processes using Azure DevOps Pipelines.

• Support application deployment and operations across Windows/IIS, virtualized and containerized environments, including Nutanix or OpenShift.

• Implement and maintain background-processing services using frameworks such as Hangfire.

• Support application security mechanisms, including ASP.NET Core Data Protection, certificate management and identity federation.

• Address vulnerabilities identified through security scanning, including Checkmarx, and penetration testing.

Application Integration & Production Support

• Integrate enterprise applications with authentication and identity-management solutions, including SAML 2.0 and Microsoft Entra ID.

• Develop and maintain integrations involving document-management systems, PDF generation and image-processing technologies.

• Provide second- and third-line application support, including incident investigation, troubleshooting and root-cause analysis.

• Support user acceptance testing (UAT), change management and release coordination through established governance processes, including Change Advisory Boards (CAB).

• Work alongside third-party contractors during application transition and support periods to ensure operational stability and continuity.

Requirements

• At least 8 years working in this field of IT with at least 6 years specifically using the mentioned tools

• A certification in UML

• A certification in Software Development - related to .NET/Microsoft technologies (Azure/C# for example)

• Strong professional experience developing and supporting enterprise applications using C#, ASP.NET Core / .NET 8 and Entity Framework.

• Proven front-end development experience with React and TypeScript.

• Solid knowledge of SQL Server, database design and application data management.

• Hands-on experience with Azure DevOps, CI/CD pipelines and application release processes.

• Understanding of multi-tier application architecture, object-oriented design and UML modelling.

• Experience working in Agile/Scrum development environments.

• Familiarity with application hosting and deployment on Windows/IIS and containerized or virtualized infrastructure.

• Experience with enterprise authentication, application security and secure development practices.

• Demonstrated ability to support production applications and resolve complex technical issues.