Full Stack C# Developer | Trading Systems | Contract Inside IR35

Investigo; Greater London; On-site; GBP 120,000 - 166,000; Full time

Job summary

Investigo in London is seeking a Senior Full Stack C# Developer to join its Front Office FX technology team, building and supporting business-critical systems used across London, New York and Singapore.

You’ll work on a modern C#/.NET platform, design REST APIs and backend services, and contribute to deal capture and post-trade processing systems while advancing messaging and event-driven architectures in a fast-paced banking environment.

Qualifications

• Proven experience in senior C#/.NET development.
• Experience building REST APIs and enterprise applications.
• Strong understanding of software architecture and design patterns.
• TDD and automated testing experience.
• Database development experience.
• Experience with large-scale, business-critical systems.

Responsibilities

• Build new features on a modern C#/.NET platform.
• Design and develop REST APIs and backend services.
• Enhance deal capture and post-trade processing systems.
• Work on messaging and event-driven architecture initiatives.
• Refactor and modernise existing applications.
• Collaborate with developers, business users and stakeholders.
• Take ownership of deliveries across the full SDL.

Skills

C#

.NET Core

REST APIs

Enterprise apps

TDD

Automated testing

Database development

Distributed systems

Tools

Kafka

IBM MQ

React

TypeScript

Python

Job description

Senior Full Stack C# Developer | Contract| Inside IR35 | London

Our investment banking clients is seeking a Senior Full Stack Developer to join its Front Office FX technology team, building and enhancing business-critical systems used across London, New York and Singapore.

This role sits within the FX Deal Capture team and is ideal for an experienced engineer who enjoys designing, building and supporting large-scale distributed applications.

You’ll work on systems responsible for trade capture, post-trade workflows and strategic enhancements used daily by traders and operational teams across the bank.

What You’ll Be Doing

• Building new features across a modern C#/.NET platform
• Designing and developing REST APIs and backend services
• Enhancing deal capture and post-trade processing systems
• Working on messaging and event-driven architecture initiatives
• Refactoring and modernising existing applications
• Collaborating with developers, business users and technology stakeholders
• Taking ownership of deliveries across the full SDL

Essential Skills

• Strong C# and .NET /.NET Core development experience
• Experience building REST APIs and enterprise applications
• Strong understanding of software architecture and design patterns
• TDD and automated testing experience
• Database development experience
• Experience working on large-scale, business-critical systems

Desirable Skills

• Kafka
• IBM MQ
• React
• TypeScript
• Python
• Front Office or financial markets experience
• AI-assisted development tools such as Claude Code, Copilot or similar