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Senior / Principal Contract Engineer – Legacy Modernisation & AI-Assisted Delivery
Contract: Full-time, initially 3 months, with likely extension
Start: Immediate – candidates should be available within 4 weeks
Location: Hybrid/Remote, with occasional presence in Dublin or London
Level: Senior / Staff / Principal Engineer
Type: Individual contributor
The Opportunity
We are looking for an experienced Senior / Principal Contract Engineer to play a key role in the modernisation of a large, long-established enterprise software platform.
This is a hands-on technical leadership role focused on safely modernising a substantial legacy codebase, establishing a robust automated testing foundation, and helping an experienced engineering team adopt an AI-assisted development lifecycle.
The platform is a large-scale desktop application with a substantial C++ codebase and a .NET API layer. The organisation is accelerating its move towards an API-first architecture, enabling functionality to be accessed through web interfaces, customer systems and automated tools.
Because the platform supports financially critical processes, the successful candidate will need to combine strong engineering fundamentals with a pragmatic and responsible approach to change, automation and AI.
Key Responsibilities
-
Build a Parity / Regression Test Harness
- Design and establish a robust test harness capable of capturing the behaviour of the existing system.
- Run current and replacement implementations against identical inputs.
- Identify and report differences between implementations.
- Create the evidence required to safely migrate functionality without introducing regressions.
- Establish automated regression coverage across a large and complex legacy system.
-
Lead AI-Assisted Engineering Adoption
- Help transition an established engineering team towards an AI-assisted development lifecycle.
- Introduce appropriate agentic development tools, workflows and engineering conventions.
- Establish practical guardrails for using AI safely within a business-critical software environment.
- Demonstrate how AI-assisted development can substantially increase engineering throughput without compromising quality.
- Help engineers develop the confidence and judgement to use AI effectively and responsibly.
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- Establish a Sustainable Engineering Practice
- Ensure the processes and tooling introduced during the engagement can be maintained by the internal engineering team.
- Develop reusable AI-agent configurations and conventions that can be maintained in source control.
- Introduce meaningful measures of delivery throughput, quality and predictability.
- Leave the team with a repeatable development and testing approach that continues beyond the contract.
What We're Looking For
Essential
- Several years of experience designing and shipping production software at Senior, Staff or Principal Engineer level.
- Experience working with large, long-lived codebases and safely introducing significant changes to them.
- Proven experience introducing automated testing into a codebase with limited existing coverage.
- Experience where software quality and reliability have significant business or financial consequences is highly valuable.
- Practical experience with AI-assisted software development, together with a thoughtful and responsible approach to its use.
- Ability to influence and change the working practices of an experienced engineering team without relying on formal authority.
- Strong communication, collaboration and technical leadership skills.
- Enthusiasm, curiosity and a genuine growth mindset.
- Right to work in the UK or Ireland.
- Availability to start within approximately four weeks.
Desirable
- Experience with one or more of the following would be advantageous:
- Characterisation testing or golden-master testing.
- Modernising legacy systems.
- Migrating towards an API-first architecture.
- Regulated, payments or other financially critical software.
- Treasury or financial software.
- C++, C# or SQL Server.
- Other comparable languages and technology stacks are also welcome — strong engineering fundamentals are more important than an exact technology match.
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You Don't Need
- You do not need previous treasury or financial-markets experience. Domain knowledge can be learned, and the existing team will provide the relevant business context.
- Management experience is also not required. This is an individual contributor role with significant technical influence and authority, but no direct reports.
Why This Role?
This is an opportunity to make a significant impact on the way a mature engineering organisation builds and modernises software.
You'll be working at the intersection of:
- Legacy system modernisation
- Automated testing and software quality
- API-first architecture
- AI-assisted engineering
- Developer productivity
- Technical transformation
The successful contractor will have the opportunity to shape both the technical approach and the engineering practices that support the next phase of the platform's evolution.
Engagement Details
- Full-time contract engagement.
- Initial 3-month contract, with extension likely.
- Hybrid working arrangement.
- Occasional attendance in Dublin or London will be required.
- Senior technical individual contributor position.
- Day-to-day work will involve close collaboration with the existing engineering leadership and development team.
If you're a senior engineer who enjoys solving difficult legacy-modernisation problems and is excited by the potential of AI-assisted development, we'd be keen to hear from you.
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