Principal Software Architect - UK Security Clearance eligibility required. Location: London, UK - Hybrid (~1-2 days per month in office / onsite) Contract: Permanent, Full-time Package: £80,000-100,000 + 10% bonus + 10% shares options + benefits About Appvia At Appvia, we help organisations modernise how they build and operate software. We are a specialist platform engineering, software, and AI enablement consultancy, delivering resilient, scalable systems that help teams move faster while maintaining quality, security, and reliability. Our work spans cloud platforms, developer experience, modern application delivery, and AI-assisted engineering practices. We partner with customers across public and private sectors to reduce technical debt, improve engineering standards, and evolve complex systems using modern software engineering approaches. Since the start of 2026, our Software Engineering practice has grown rapidly into a dedicated team supporting large-scale modernisation programmes across public and private sectors, and we’re continuing to invest heavily in growing the capability further. About the Role As a Principal Software Architect, you will be the architectural voice within our software engineering engagements: owning solution design, shaping technical direction, and constructively challenging both the business and technical architecture of the systems we help modernise. Domain Driven Design sits at the heart of how we approach this. You will lead the domain modelling that underpins our solutions, working with customer stakeholders and domain experts to build a shared understanding of the business, establish a ubiquitous language, and translate that into well-defined bounded contexts, service boundaries, and system decomposition. Where a customer's existing architecture doesn't reflect their domain, you'll make the case for change and lead it. This is a hands-on role. You'll spend most of your time developing alongside the team, but you'll be doing so while driving the solution: ensuring the domain model is expressed faithfully in the code, making and documenting architectural decisions, and ensuring what we build is coherent, evolvable, and aligned to the customer's business goals, not just well-engineered in isolation. You will work closely with delivery managers, platform engineers, customer architects, and senior stakeholders to influence decisions that sit above the codebase: system decomposition, integration strategy, domain modelling, and the trade-offs between business need and technical direction. You'll also help lead and grow the team, and contribute to Appvia's broader engineering strategy by shaping the architectural patterns, DDD practices, standards, and AI-assisted engineering approaches we apply consistently across customer engagements. Interview Process - 3 Stage Discovery conversation with Talent Acquisition Technical & Architecture Interview with the Engineering Team Final Interview with Leadership Important You must be eligible for UK Security Clearance (SC) : British Passport or ILR Resided in the UK for the last 5 years No criminal record or financial irregularities Requirements About You You are an architecturally minded senior engineer: someone who thinks in domains, systems, and trade-offs, but who has never stopped coding. You believe that good architecture starts with a deep understanding of the business domain, and you're energised by shaping the why and what of a solution as much as the how. You're comfortable challenging established thinking with customers in a consulting environment, earning influence through credibility, clarity, and delivery. You'll bring: Deep, practical experience applying Domain Driven Design on real systems: strategic design (bounded contexts, context mapping, ubiquitous language) as well as tactical patterns (aggregates, domain events, anti-corruption layers) and knowing when each is warranted. Experience leading collaborative domain discovery with business stakeholders, using techniques such as Event Storming, domain storytelling, or similar. Strong architectural judgement, with a track record of owning and driving solution design on complex systems, not just contributing to it. Proven delivery of microservice-based architectures where service boundaries were derived from the domain, including the hard parts: data ownership, integration patterns, and evolving boundaries as understanding of the domain deepens. The ability to understand a customer's business architecture, connect it to technical decisions, and constructively challenge it when it doesn't serve the outcome. Confidence communicating and defending architectural decisions to senior stakeholders, and documenting them clearly (e.g. ADRs, C4 or similar). Strong hands-on full-stack development skills. You lead from within the codebase. Experience improving engineering effectiveness through testing strategy, automation, and developer tooling. Exposure to AI-assisted development approaches to improve code quality and productivity. Confidence mentoring engineers and growing domain-driven and architectural thinking across a team. A consulting mindset, able to translate business problems into practical technical solutions. Experience in regulated or public sector environments is beneficial but not required. Responsibilities Own the architecture and solution design of modern, scalable software systems across customer engagements. Lead domain discovery and modelling with customers, establishing bounded contexts, a ubiquitous language, and a shared understanding between business and engineering. Shape and challenge business and technical architecture: service boundaries, domain models, dependencies, and integration strategy across complex systems. Ensure the domain model is reflected in the software itself, keeping code, architecture, and business understanding aligned as systems evolve. Act as a trusted architectural advisor to customers, guiding decision-making, articula