Senior C# Developer

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 GitHub 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 GitHub 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 GitHub 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 - UTC+1 (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

GitHub

Automated Testing Frameworks

GitHub 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 https://www.allegisgroup.com/en-gb/privacy-notices.

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 https://www.allegisgroup.com/en-gb/privacy-notices.

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 exercise your privacy rights, please visit the "Contacting Us" section of our Online Privacy Notice at https://www.allegisgroup.com/en-gb/privacy-notices for details on how to contact us. To protect your privacy and security, we may take steps to verify your identity, such as a password and user ID if there is an account associated with your request, or identifying information such as your address or date of birth, before proceeding with your request. If you are resident in the UK, EEA or Switzerland, we will process any access request you make in accordance with our commitments under the UK Data Protection Act, EU-U.S. Privacy Shield or the Swiss-U.S. Privacy Shield.