Senior Full Stack Developer (.Net, JS) in London

Vialto is a market leader in global mobility services. We are unique and the only stand-alone global mobility business. Our teams help companies streamline and effectively manage their global mobility programs in a cost-efficient and compliant manner. Our services focus on providing cross-border compliance and risk assessment for tax, immigration, business travel, rewards and compensation, and remote work. Vialto is unstoppable when we work together in a culture of belonging, where everyone can thrive.

Vialto is hiring a Senior Full Stack Engineer to design, build, and operate secure, scalable products that power our Compensation Collection, Shadow Payroll, and Equity offerings for the world's most complex multinational employers. This role is for an experienced engineer who can own end-to-end features—from cross-border compensation data ingestion to shadow payroll calculation engines to equity event processing—contribute to architectural decisions and consistently deliver production-ready solutions using agentic development practices.

What You'll Do

• Build and evolve modern web experiences for Compensation Collection, Shadow Payroll, and Equity products using Next.js, React, and TypeScript with a focus on performance, reliability, and clarity for tax, payroll, and mobility operators.
• Design and implement backend services and APIs using C#, .NET, and WebAPI to support compensation data ingestion, cross-border payroll calculations, equity event processing, and integrations with client HR, payroll, and equity administration systems.
• Deliver Azure-native implementations of shadow payroll calculation engines, compensation aggregation pipelines, and equity tax event workflows using Microsoft PaaS services, secure patterns, and operational best practices.
• Contribute to system architecture and technical design for multi-country payroll, compensation, and equity domains.
• Own production readiness for your work including logging, monitoring and alerting, reconciliation tooling, incident response support, and operational documentation.
• Apply secure development practices appropriate for handling sensitive compensation, payroll, and equity data.
• Partner with product, mobility tax, payroll, and equity subject-matter experts to translate complex regulatory and client requirements into technical plans and deliverables.
• Use agentic development practices including agent-driven development with Claude Code, Codex, or similar AI coding agents.
• Work in a spec-driven development workflow, authoring detailed specifications.
• Design and implement AI-powered features within Compensation Collection, Shadow Payroll, and Equity products.
• Evaluate, integrate, and operationalize AI APIs, models, and toolchains within application architectures.
• Mentor and support other engineers through code reviews, pairing, and technical guidance.

Required Qualifications

• 5+ years professional software development experience building enterprise web applications and services.
• Strong experience designing and building large JavaScript applications with Next.js and/or React.
• Strong backend development experience in C# and .NET.
• Proven experience with Microsoft Azure designing and building cloud solutions.
• Experience delivering systems in regulated or compliance-oriented environments.
• Strong engineering fundamentals including design patterns and scalable architecture.
• Experience with agentic or AI-assisted development workflows.
• Demonstrated ability to build products that incorporate AI capabilities.

Preferred Qualifications

• Direct experience building or integrating with payroll, shadow payroll, compensation collection, equity administration, or global mobility tax platforms.
• Familiarity with cross-border compensation concepts.
• Experience integrating with HCM, payroll, and equity systems.
• Azure certifications and/or Microsoft certifications.
• Experience with event-based and distributed systems.
• Data and persistence experience with SQL Server and ORMs.
• Strong testing discipline including TDD and BDD.
• Experience building analytics and reporting with BI and data visualization tools.

Technical Skills We Value

• Frontend: Next.js, React, TypeScript, HTML, CSS.
• Backend: C#, ASP.NET, WebAPI.
• Cloud: Azure PaaS services.
• Domain: Compensation Collection workflows, Shadow Payroll calculation and reporting.
• Engineering practices: Git-based workflows, secure SDLC.
• AI-enabled delivery: agentic development using Claude Code, Codex, or similar AI coding agents.

What Success Looks Like

• Delivers complex Compensation Collection, Shadow Payroll, and Equity features end-to-end with high quality.
• Produces clean, maintainable code with strong test coverage.
• Identifies and resolves performance, reliability, accuracy, and security issues.
• Contributes meaningfully to architecture and raises standards through code reviews.

Education

• Bachelor's degree in computer science, Engineering, or related field required.
• Master's degree preferred.

Why This Role

You'll help build and scale the technology behind Compensation Collection, Shadow Payroll, and Equity—the engines that keep globally mobile employees of the world's largest multinationals paid accurately, taxed correctly, and compliant across dozens of jurisdictions.