Senior .Net Developer (Billing Systems Essential) in Hampshire, Portsmouth

2 Year Fixed Term Contract in Southampton, 3 days per week. £60-65k + 10% Bonus, 8% Pension, Private Medical.

This role cannot offer Visa Sponsorship. You must have Billing Systems or Financial Product Experience to apply.

Your new company: I'm recruiting exclusively for a globally connected business operating at the heart of international trade. Their name is known worldwide with over 100k employees following recent acquisitions and you'll join initially on a 2-year Fixed Term Contract. With a significant multi-year Billing Transformation Programme underway, the business is replacing a complex legacy billing platform with a modern enterprise solution. This is a high-impact programme with strong investment to modernise and the chance to introduce AI in production. It's the best of both worlds, security of a multi-national with the strong collaboration and interaction of an SME. This role is hybrid, with a minimum of 3 days in their Southampton office.

Your new role: This is not a typical greenfield development role. You'll sit at the heart of a complex billing environment, working across system stabilisation, reverse engineering and transformation support. The role is best suited to someone who enjoys understanding how systems truly work, not just building new features. A large part of your time will involve working on a heavily customised, customer-specific billing platform, where logic can vary significantly between clients. You'll analyse existing code, uncover undocumented behaviours and translate this into clear documentation and understanding for both technical and business teams. You'll work closely with Billing SMEs, Business Analysts and programme stakeholders, acting as the bridge between technical implementation and real-world billing processes. Alongside this, you'll support ongoing changes and enhancements, ensuring anything delivered today aligns with the longer-term transition to a new enterprise billing system. There is also a strong focus on modern engineering practices, including the use of AI-assisted tooling to improve understanding, documentation and delivery across a complex environment.

What you'll need to succeed: You'll be a strong .NET Developer with experience working on complex or business-critical systems within billing/invoicing or on transactional financial products where the system is tailored to different customers' needs. The key requirement is the ability to take ownership of an existing system. This means being comfortable reading and understanding legacy code, troubleshooting issues and explaining behaviour to non-technical stakeholders. You'll have solid experience across C# / .NET and SQL Server and APIs, alongside an understanding of how systems integrate and handle complex data. Exposure to containerisation (Docker) and modern DevOps practices will also be important. Experience working in reverse engineering of existing applications, transformation programmes, modernisation initiatives or environments with limited documentation would be highly beneficial, as would experience working with AI-assisted Engineering tools like Claude or CoPilot in production.

What you'll get in return: You'll be joining a business where the systems you build have real-world impact at scale. This is an opportunity to influence both the technical direction and the culture of a team, within an organisation that is actively investing in its technology capability. You'll benefit from a hybrid working model, a guaranteed 10% bonus, 8% pension match, private healthcare, life assurance and 25 days holiday plus bank holidays.

What you need to do now: At Hays Technology, we are shaping the future of recruitment. The rapid adoption of cloud, which is making customer interfaces more engaging and creating a seamless engagement with businesses, means that from the foundation of your organisation up, software developers are critical to success. As the competition for talent grows, we're ready and waiting to help developers really make an impact on organisations, so talk to us today. We are Hays Technology. To find out more and to be considered for this position please apply directly, or contact Max Wilcock, Senior Business Director on 0333 010 5724.