December 17, 2025

.NET Developer

Senior • Hybrid

Warsaw, Poland

Sii ensures that all employment-related decisions are made solely on the basis of qualifications and competencies. We are committed to equal treatment of all individuals, regardless of any protected characteristics, and promoting a diverse and inclusive work environment.


We are looking for a .NET Developer to join the front-office Trading Tool team that builds and maintains high-performance applications used by traders for market-making. You will work on a complex system combining WPF/DevExpress interfaces, browser-based tools, and integrations with multiple internal APIs. The team operates in a distributed setup between France and Poland.


The role requires working from the Warsaw office two to three days per week.


Your tasks

  • Design, develop, test, and deploy high-performance trading applications operating in a multi-threaded environment

  • Build and maintain WPF/DevExpress user interface components used by traders

  • Translate technical and functional requirements into detailed user stories and collaborate closely with Agile Masters and Business Analysts

  • Deliver and support applications through Continuous Delivery (DevOps)

  • Maintain and improve production support tools and participate in non-regression testing

  • Recommend and implement improvements to application performance, architecture, and development processes

  • Provide clear and consistent progress updates to traders and stakeholders


Requirements

  • Minimum 5 years of experience in backend C# development

  • Strong understanding of multithreaded programming and microservices architecture

  • Experience with WPF/DevExpress

  • Fluency in English (spoken and written)

  • Excellent communication and teamwork skills

  • Proactive, solution-oriented, and collaborative mindset

  • Open to a hybrid work model (2-3 days per week on-site)

  • Fluent in Polish required

  • Residing in Poland required


What we offer 

  • Great Place to Work since 2015 - it’s thanks to feedback from our workers that we get this special title and constantly implement new ideas 

  • Employment stability - revenue of PLN 2.1BN, no debts, since 2006 on the market 

  • We share the profit with Workers - over PLN 76M has already been allocated for this aim since 2022 

  • Attractive benefits package - private healthcare, benefits cafeteria platform, car discounts and more 

  • Comfortable workplace – class A offices or remote work 

  • Dozens of fascinating projects for prestigious brands from all over the world 

  • PLN 1 000 000 per year for your ideas - with this amount, we support the passions and voluntary actions of our workers 

  • Investment in your growth – meetups, webinars, training platform and technology blog – you choose 

  • Fantastic atmosphere created by all Sii Power People 


Join the Sii team – develop your skills, gain experience, and build your career!