Senior Full Stack .NET Developer – C#, React & Azure

Us3 Consulting; Warszawa; On-site; PLN 180,000 - 260,000; Full time

Job summary

Us3 Consulting is seeking a Senior Full-Stack .NET Developer to deliver end-to-end business features across backend APIs, frontend applications, databases, and cloud-connected services.

You will work across the full application stack, building robust solutions with C#, .NET, ASP.NET Core, React, TypeScript, SQL/NoSQL databases, and cloud services. This is a hands-on role suited to someone who can independently take complex features from design through to production.

Qualifications

• Proven experience in C# and .NET development.
• Strong ASP.NET Core Web API experience.
• Solid React and TypeScript skills with independent feature delivery.

Responsibilities

• Design and implement backend APIs and business logic using C# and ASP.NET Core.
• Build and integrate frontend functionality using React and TypeScript.
• Work with SQL and NoSQL databases, including data modelling and query optimisation.
• Deliver complete features across backend, frontend, database, and integration layers.
• Troubleshoot and resolve production issues across multiple application layers.
• Contribute to code reviews, testing, and overall technical quality.
• Integrate with external systems and cloud services.
• Apply secure development practices, including secure API design and tenant-boundary awareness.

Skills

C# & .NET

ASP.NET Core Web API

React & TypeScript

SQL/NoSQL databases

Cloud fundamentals

Debugging & problem-solving

Application security awareness

Independent end-to-end delivery

Tools

MongoDB

Azure SQL

Azure App Services

Job description

We’re looking for a Senior Full-Stack .NET Developer to deliver end-to-end business features across backend APIs, frontend applications, databases, and cloud-connected services.

You’ll work across the full application stack, building robust solutions with C#, .NET, ASP.NET Core, React, TypeScript, SQL/NoSQL databases, and cloud services. This is a hands-on role suited to someone who can independently take complex features from design through to production.

What you’ll do

• Design and implement backend APIs and business logic using C# and ASP.NET Core.
• Build and integrate frontend functionality using React and TypeScript.
• Work with SQL and NoSQL databases, including data modelling and query optimisation.
• Deliver complete features across backend, frontend, database, and integration layers.
• Troubleshoot and resolve production issues across multiple application layers.
• Contribute to code reviews, testing, and overall technical quality.
• Integrate with external systems and cloud services.
• Apply secure development practices, including secure API design and tenant-boundary awareness.

Essential skills

• Strong C# and .NET development experience.
• Strong ASP.NET Core Web API experience.
• Solid React and TypeScript skills, with the ability to independently build and modify routine screens.
• Experience with SQL and/or NoSQL databases, with the ability to learn the other quickly.
• Understanding of cloud fundamentals.
• Strong debugging, problem-solving, and analytical skills.
• Good awareness of application security and common vulnerabilities.
• Ability to work independently on complex, end-to-end development tasks.

Preferred skills

• MongoDB and Azure SQL experience.
• Experience with Azure App Services, Storage, Key Vault, and monitoring.
• Experience in financial, tax, compliance, or other regulated platforms.
• Experience supporting frontend modernisation in enterprise environments.
• Experience with Motif, design-system migration, or enterprise UI transitions.