Senior Software Engineer, .NET & WCF Modernization

Position Overview The Senior Software Engineer, .NET & WCF is responsible for supporting, enhancing, and modernizing a portfolio of business-critical .NET Framework and WCF-based applications. This role combines hands-on development, production support, technical leadership, and modernization planning to ensure legacy platforms remain stable, secure, and scalable while evolving toward modern .NET and cloud-ready architectures. The successful candidate will work closely with Product, QA, DevOps, and Architecture teams to maintain existing services, resolve complex technical issues, improve performance, and lead the gradual transformation of legacy applications into modern API-driven solutions. Key Responsibilities Legacy Application Support & Enhancement Support, maintain, and enhance existing .NET Framework and WCF-based applications and services. Diagnose and resolve complex production and application issues across multiple environments. Analyze system behaviour, logs, and performance metrics to identify root causes and implement fixes. Develop new functionality within existing applications while maintaining system stability and backward compatibility. Participate in on-call support and critical incident resolution activities as required. Document system behavior, integrations, technical dependencies, and support procedures. WCF Services & Integration Engineering Design, develop, and maintain WCF services supporting internal and external business processes. Support SOAP-based integrations and XML messaging frameworks. Troubleshoot service communication, security, serialization, and interoperability issues. Manage service contracts, endpoint configurations, bindings, and authentication mechanisms. Work with business and technical stakeholders to support enterprise integration requirements. Ensure integrations remain reliable, secure, and scalable. Modernization & Migration Initiatives Assess legacy applications and identify modernization opportunities. Develop phased migration strategies from WCF services to Core Web APIs and modern service architectures. Refactor legacy code to improve maintainability, performance, and testability. Modernize authentication, authorization, and service communication patterns. Support migration efforts from .NET Framework to modern .NET versions where appropriate. Evaluate technical debt, prioritize modernization efforts, and recommend implementation approaches. Application Development Develop and maintain applications using C#, .NET Framework, , Core, and related technologies. Build and enhance RESTful APIs supporting modernization initiatives. Implement secure, maintainable, and scalable software solutions. Apply software design principles including SOLID, dependency injection, and clean code practices. Contribute to application architecture and technical design discussions. Database Development & Performance Design, develop, and maintain SQL Server database objects including: Stored procedures Functions Views Triggers Indexes Troubleshoot data-related issues and optimize database performance. Analyze execution plans and improve query efficiency. Support application reporting, integration, and data exchange requirements. Collaborate with DBAs on database design, maintenance, and performance improvements. Technical Leadership Provide technical guidance and mentorship to developers. Conduct code reviews and promote engineering best practices. Identify technical risks and propose mitigation strategies. Assist in establishing development standards and modernization roadmaps. Collaborate with architects to align modernization efforts with long-term platform goals. DevOps & Continuous Improvement Support CI/CD pipelines and deployment automation activities. Improve build, deployment, and release processes. Collaborate with QA teams to increase automated testing coverage. Contribute to monitoring, logging, and observability improvements. Recommend tooling and process enhancements that improve development efficiency and platform reliability. Skills & Qualifications Required 7+ years of software development experience using Microsoft technologies. Strong experience with C#, .NET Framework, and WCF services. Experience supporting and enhancing large-scale legacy enterprise applications. Strong understanding of SOAP, XML, XSD, and service-oriented architectures. Experience developing REST APIs using Core or Web API. Experience designing and implementing modernization strategies for legacy systems. Strong SQL Server experience including: Stored procedures Query optimization Performance tuning Database design Experience troubleshooting production issues and performing root-cause analysis. Strong understanding of software design principles and object-oriented development. Experience with source control systems such as Git. Experience working in Agile development environments. Preferred Experience migrating WCF services to Core Web APIs or gRPC. Experience modernizing .NET Framework applications to .NET 8+. Experience with Azure services including App Services, Service Bus, Key Vault, and Application Insights. Experience with Docker and container-based deployments. Experience implementing CI/CD pipelines using Azure DevOps or GitHub Actions. Experience with event-driven architectures and messaging technologies. Familiarity with Domain-Driven Design (DDD) and microservices architecture. Experience with observability platforms, distributed tracing, and application monitoring. Bachelor's degree in Computer Science, Engineering, or equivalent practical experience. Career Stage: Senior Associate London Stock Exchange Group (LSEG) Information: Join us and be part of a team that values innovation, quality, and continuous improvement. If you're ready to take your career to the next level and make a significant impact, we'd love to hear from you. LSEG is a leading global financial markets infrastructure and data provider. Our purpose is driving financial stability, empowering economies and enabling customers to create sustainable growth. Our purpose is the foundation on which our culture is built. Our values of Integrity, Partnership , Excellence and Change underpin our purpose and set the standard for everything we do, every day. They go to the heart of who we are and guide our decision making and everyday actions. Working with us means that you will be part of a dynamic organisation of 25,000 people across 65 countries. However, we will value your individuality and enable you to bring your true self to work so you can help enrich our diverse workforce. We are proud to be an equal opportunities employer. This means that we do not discriminate on the basis of anyone’s race, religion, colour, national origin, gender, sexual orientation, gender identity, gender expression, age, marital status, veteran status, pregnancy or disability, or any other basis protected under applicable law. Conforming with applicable law, we can reasonably accommodate applicants' and employees' religious practices and beliefs, as well as mental health or physical disability needs. You will be part of a collaborative and creative culture where we encourage new ideas. We are committed to sustainability across our global business and we are proud to partner with our customers to help them meet their sustainability objectives. Our charity, the LSEG Foundation provides charitable grants to community groups that help people access economic opportunities and build a secure future with financial independence. Colleagues can get involved through fundraising and volunteering. LSEG offers a range of tailored benefits and support, including healthcare, retirement planning, paid volunteering days and wellbeing initiatives. Please take a moment to read this privacy notice carefully, as it describes what personal information London Stock Exchange Group (LSEG) (we) may hold about you, what it’s used for, and how it’s obtained, your rights and how to contact us as a data subject . If you are submitting as a Recruitment Agency Partner, it is essential and your responsibility to ensure that candidates applying to LSEG are aware of this privacy notice.