Senior C# Engineer – .NET 8/9, AWS Lambda, SQS, SNS – Outside IR35 at Smart Sourcer Limited, City of London, £Contract Rate

Senior C# Engineer – .NET 8/9, AWS Lambda, SQS, SNS – OUTSIDE IR35

£700–£800/day • 100% Remote • 11-month rolling contract

Takeaway: Lead the architecture and build of a greenfield SaaS platform as a deeply senior, hands-on C# engineer, with heavy emphasis on deep .NET engineering, high-performance distributed systems, and real-world AWS serverless delivery. You’ll also have the opportunity to develop hands-on skills with Claude Code, one of the most advanced AI-assisted development tools in the industry.

Role Overview:

You’ll operate as the technical spearhead for a greenfield product build, reporting to the Director of Engineering. Expect deep backend engineering, distributed system design, and high-quality serverless delivery, plus the chance to adopt modern AI-assisted development practices as part of your workflow.

What You’ll Bring:

• Senior/Staff-level backend mastery in C# and .NET 8/9, with the ability to architect and lead distributed REST microservices at scale.
• Strong authority in AWS serverless engineering: Lambda-first mindset, hands-on experience with API Gateway, SQS, Step Functions, EventBridge and IAM.
• Deep data expertise across Aurora MySQL and DynamoDB: schema design, access patterns, indexing, query tuning, and pragmatic trade-offs around consistency, scale and cost.
• Real-world experience designing event-driven systems with SQS: idempotency, retries, ordering, DLQs and operational resilience.
• Strong API design sensibility: versioning, documentation, throttling, backwards compatibility, and a genuine obsession with developer experience.
• Product-first mindset: comfortable shaping requirements, partnering with BAs, and operating without a traditional PO.
• 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.
• 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.
• Developing hands-on skills with Claude Code, including AI-assisted development patterns, smart refactoring, automated context management and productivity-boosting workflows.

Contract Details:

• £700–£800/day
• Outside IR35
• 100% remote (UK)
• 11-month rolling contract