Senior C# Developer

Location: South Kensington

Description Project Overview TEKsystems Global Services is supporting a strategic product engineering initiative within a leading global software organisation. We are seeking an experienced Senior C# Developer to contribute to the modernisation and expansion of cloud-connected capabilities across key French product offerings. The successful consultant will play a critical role in designing and developing GraphQL APIs for Sage 50 and Sage 100 products, leveraging existing SDKs and integrating with the Sage Copilot Factory Framework.

This work forms part of a broader programme aimed at enhancing product connectivity, automation, AI enablement, and developer experience across the French product portfolio. This engagement requires a fluent French speaker who is comfortable working within distributed international teams across the European time zone and collaborating with product, architecture, and engineering stakeholders.

Key Responsibilities:

Design, develop, and maintain GraphQL APIs for Sage 50 and Sage 100 products. Build and execute automated testing frameworks to ensure API quality and reliability. Integrate existing local SDK capabilities into modern cloud-connected services. Contribute to the integration of Sage 50 and Sage 100 products with the Sage Copilot Factory Framework. Develop scalable and secure backend services using C# and .NET

Core. Collaborate with architects, product teams, and engineering stakeholders to define API contracts and technical solutions. Participate in code reviews and promote engineering best practices. Utilise Git Hub and modern development tooling to support CI/CD and software delivery processes. Support cloud-native development and deployment activities within Microsoft Azure. Required

Skills & experience Essential Strong commercial experience developing applications using C# and .NET Core Proven experience designing and building GraphQL APIs experience creating and maintaining automated tests Strong understanding of Microsoft Azure Proficiency with Microsoft Visual Studio experience using Git Hub for source control and collaborative development experience working within Agile software engineering environments Fluent spoken and written French Strong communication and stakeholder engagement skills Desirable experience integrating with existing SDKs or legacy product platforms Exposure to AI-enabled products and developer frameworks experience of Git Hub Copilot/Codex or modern AI-assisted development tools Understanding of API security, authentication, and performance optimisation Previous experience working within SaaS or product engineering organisations Engagement Details Location
- Remote / Europe Language Requirement
- Fluent French Time Zone - UTC1 (France, Germany, Spain) Start Date - 1 October 2026 End Date - 30 September 2027 Contract Length - 11 Months Engagement Type
- Contract Consultant Technology Stack C# .NET Core GraphQL Microsoft Azure Microsoft Visual Studio Git Hub Automated Testing Frameworks Git Hub Copilot / Codex REST/API Integration Desired Profile We are looking for a Senior-level engineer who combines deep Microsoft development expertise with modern API design experience. The ideal consultant will have a strong product engineering mindset, be comfortable working with complex existing codebases and SDKs, and possess the communication skills required to engage effectively with French-speaking stakeholders across the business and engineering teams.

The role supports the delivery of next-generation cloud connectivity, GraphQL services, and AI-enabled product integration capabilities for the French Sage product portfolio. Skills C# .Net Core French GRAPHql API Azure Github Codex

Job Title:

Senior C# Developer

Location:

Newcastle upon Tyne, UK Job Type: Contract Trading as TEKsystems. Allegis Group Limited, Maxis 2, Western Road, Bracknell, RG12 1RT
, United Kingdom. No. 2876353. Allegis Group Limited operates as an Employment Business and Employment Agency as set out in the Conduct of Employment Agencies and Employment Businesses Regulations 2003. TEKsystems is a company within the Allegis Group network of companies (collectively referred to as "Allegis Group"). Aerotek, Aston Carter, EASi, Talentis Solutions, TEKsystems, Stamford Consultants and The Stamford Group are Allegis Group brands.

If you apply, your personal data will be processed as described in the Allegis Group Online Privacy Notice available at  To access our Online Privacy Notice, which explains what information we may collect, use, share, and store about you, and describes your rights and choices about this, please go to  We are part of a global network of companies and as a result, the personal data you provide will be shared within Allegis Group and transferred and processed outside the UK, Switzerland and European Economic Area subject to the protections described in the Allegis Group Online Privacy Notice.

We store personal data in the UK, EEA, Switzerland and the USA. If you would like to…