Senior C# Engineer - Agentic Engineering, .NET 9, AWS Lamba & SQS
Posted Today by Smart Sourcer Limited
£800 Per day
Outside
Remote
City of London (EC1)
Summary: The Senior C# Engineer will lead the development of a greenfield SaaS product, focusing on AI-native engineering and complex distributed systems. This role requires a hands-on approach, with responsibilities including architecture design and driving engineering standards. The position is fully remote and offers a competitive daily rate. The ideal candidate will possess deep expertise in C# and AWS technologies, along with a product-centric mindset.
Key Responsibilities:
- Architecting, building and shipping complex, high-performance distributed services in C#/.NET 8/9 on AWS Lambda.
- Designing and delivering resilient event-driven systems using SQS and related AWS messaging primitives.
- Embedding AI-native engineering and agentic workflows into everyday delivery.
- Owning features end-to-end, including product thinking, scoping, trade-offs, sequencing, and delivery.
- Designing clean, well-versioned, well-documented APIs.
- Championing a high-quality engineering culture with a focus on testing, peer review, CI/CD, observability, performance, and secure coding.
Key Skills:
- Senior/Staff-level backend engineering depth in C# and .NET 8/9.
- Strong authority in AWS serverless technologies, including Lambda, API Gateway, SQS, Step Functions, EventBridge, and IAM.
- Practical experience with Claude Code or similar and advanced agentic workflows.
- Deep data expertise across Aurora MySQL and DynamoDB.
- Proven ability to design event-driven systems with SQS.
- Strong API design sensibility.
- Excellent communication skills and confidence in client interaction.
- Rigorous engineering standards including Git-based workflows and CI/CD.
- Pragmatic, outcome-oriented approach with comfort in ambiguity.
Salary (Rate): £800/day
City: City of London
Country: United Kingdom
Working Arrangements: remote
IR35 Status: outside IR35
Seniority Level: Senior
Industry: IT
Senior C# Engineer (AI-Native & Agentic Engineering) – .NET 8/9, AWS Lambda/SQS – OUTSIDE IR35
£750–£800/day • 100% Remote • 11-month rolling contract
A rare opportunity to lead the build of a greenfield SaaS product as a deeply senior, hands-on C# engineer. Reporting directly to the Director of Engineering, you’ll operate as the technical spearhead; shaping architecture, driving AI-native engineering patterns, and delivering complex distributed systems at pace.
We’re looking for someone who is product-centric, agentic-minded, and thrives in ambiguity. If you enjoy solving hard problems, owning outcomes end-to-end, and setting the engineering bar for others, this one’s for you.
What You’ll Bring:
- Senior/Staff-level backend engineering depth in C# and .NET 8/9, with the ability to architect and lead distributed REST microservices at scale.
- Strong authority in AWS serverless: Lambda-first, with hands-on experience across API Gateway, SQS, Step Functions, EventBridge and IAM.
- Practical experience with Claude Code (or similar) and advanced agentic workflows — multi-agent orchestration, context management, custom commands/skills, and scaling AI-assisted delivery.
- Deep data expertise across Aurora MySQL and DynamoDB — schema design, access patterns, indexing, query tuning, and pragmatic trade-offs around consistency, scale and cost.
- Proven ability to design event-driven systems with SQS: idempotency, retries, ordering, DLQs and operational robustness.
- Strong API design sensibility: versioning, documentation, throttling, backwards compatibility and a genuine obsession with developer experience.
- A product-first mindset — comfortable operating without a traditional PO, partnering with BAs, shaping requirements and owning delivery.
- Excellent communication skills and confidence in ad-hoc client interaction.
- Rigorous engineering standards: Git-based workflows, trunk-based development, CI/CD (GitHub Actions), IaC (CDK/Terraform), comprehensive testing and secure-by-default coding.
- Pragmatic, outcome-oriented, comfortable with ambiguity and biased toward shipping.
What You’ll Own:
- Architecting, building and shipping complex, high-performance distributed services in C#/.NET 8/9 on AWS Lambda.
- Designing and delivering resilient event-driven systems using SQS and related AWS messaging primitives.
- Embedding AI-native engineering and agentic workflows into everyday delivery — orchestrating sub-agents, managing context, and running parallel workstreams.
- Owning features end-to-end: product thinking, scoping, trade-offs, sequencing and delivery.
- Designing clean, well-versioned, well-documented APIs that other engineers love to consume.
- Championing a high-quality engineering culture: testing discipline, peer review, CI/CD excellence, observability, performance and secure coding.
Contract Details
£750–£800/day
Outside IR35
100% remote (UK)
11-month rolling contract