Principal Software Engineer

Location: London / gb

As a Principal Software Engineer, your goal is to make engineering, and our engineers, better every day. You are approachable and collaborative, and you actively nurture a diverse and inclusive workplace.

You work closely with engineering teams to sharpen their practices, processes and technology, and to explore new ones. You help them clear technical hurdles of any size, and when it helps, you roll up your sleeves and build alongside them.

Your work spans the full stack: our customer-facing apps and web, and the .NET microservices, APIs and data behind them. You will help teams build consistent, reliable experiences end to end, and you will keep growing your own range as you go.

You will help lead ASOS into the age of agentic commerce. AI agents are changing how people discover, compare and buy fashion, and you will be at the centre of how we respond. You will turn bold ideas into working proofs of concept, work alongside leading names in the industry, and bring the best of it to life in the products millions of customers use every day.

Key Responsibilities

Accelerating our agentic commerce journey

Prove it fast. Lead rapid proofs of concept that test how AI agents can discover, recommend and buy fashion through ASOS. Go from idea to working prototype in weeks, learn from real results and move on quickly from what does not work.

Work with the best. Build relationships with industry leaders, including technology partners, AI platform providers and industry groups. Bring their thinking into ASOS and make sure ASOS has a voice in how agentic commerce develops.

Build the foundations. Shape the technical groundwork agents will rely on: agent-ready APIs, rich product and catalogue data, identity, payments, and guardrails for trust, security and privacy. Keep ASOS aligned with emerging agent standards and protocols.

Make change happen. Take what works from prototype to production with the teams who will own it, so promising ideas become secure, reliable and observable customer experiences.

Bring people with you. Share demos, findings and practical guidance across the engineering community, and help colleagues build confidence with agentic technology.

Stay responsible. Champion responsible AI. Customer trust, data protection and transparency come first in everything we try.

Technical leadership

• Be a technical authority across front-end and back-end systems: guide teams, solve problems, review and underwrite designs, and act as the point of escalation for the toughest engineering challenges.
• Work across codebases and platforms to level up each one, using shared best practice and consistent architecture where it makes sense.
• Own and evolve the architecture of our front-end and microservice landscape. Set direction, make and record sound architectural decisions, and weigh trade-offs clearly. Shape how front ends and back ends fit together, including API design, contracts, integration patterns and the boundaries between teams and services.
• Design for scale. Make sure our systems stay fast, available and cost-effective through peak trading periods and as the business grows.
• Champion performance, reliability, security and accessibility in everyday delivery, from the customer's device through to our services and infrastructure.

Engineering practices and productivity

• Work with product development teams to make it as easy as possible to commit code that follows our guidelines.
• Partner with peers to find and introduce tools, technologies and ways of working that raise the quality and productivity of ASOS Engineering.
• Evaluate and introduce AI-assisted development tools, with clear guidance on security, code review and quality.
• Define and champion good engineering practice across the community, refining existing approaches and suggesting new ones.

Quality and delivery

• Make sure software going into production meets ASOS standards: well tested, observable, secure and of high quality. Use monitoring and telemetry to guide decisions.
• Build and sustain highly productive teams focused on delivery, through strong collaboration and ownership.

People and skills

• Grow engineers across the stack through mentoring, pairing and learning sessions, so more people can work confidently across front-end and back-end systems.

About you

We appreciate that you may not tick all of the technical boxes listed below. If you feel like you have the right experience for the job, but don't hit every piece of criteria, we would still encourage you to apply!

• A highly experienced, senior engineer with a proven record of guiding multi-discipline teams through the full delivery lifecycle of complex, large-scale, distributed software systems.
• Deep, hands-on experience building back-end systems in .NET (C#), including REST APIs and microservices, with the ability to pick up new languages and tools quickly.
• Comfort traversing front-end technologies across web and apps. You do not need to be a specialist in all of them, but you can read, review and contribute to front-end code and guide the teams who own it.
• Strong experience with microservices and distributed systems, including event-driven and asynchronous designs, service boundaries, resilience, and running them in production.
• Hands-on experience building with AI, such as large language models or agents, or a strong appetite to learn fast and apply it in a commerce setting.
• A track record of prototyping quickly, then hardening what works for production.
• Confidence working with external partners and industry groups, and explaining complex technical ideas clearly to senior stakeholders.
• Enterprise-level experience building and running systems at scale: high-traffic, high-availability platforms serving millions of users, with a strong grasp of scalability, performance, resilience and cost at that size.
• Excellent architecture skills. You have designed and evolved complex systems, can explain and defend your decisions to engineers and senior stakeholders, and manage technical debt and dependencies over time.
• Solid understanding of sync and async design patterns for enterprise integration and data, which are crucial for reliable, resilient, high-performance systems.
• Experience with Agile and XP practices, and with helping teams get the most from their preferred approach.
• Deep understanding of the software development lifecycle, including quality assurance, build and deployment (CI/CD and progressive releases), and monitoring and telemetry.
• Familiarity with the best tools and practices for each phase of delivery, such as unit testing, TDD, BDD, integration testing and performance testing.
• Awareness of application security fundamentals, including authentication, secure data handling and API protection.
• Experience designing and running cloud-native systems, ideally on Microsoft Azure.

BeneFITS’

• Employee discount (hello ASOS discount!)
• Employee sample sales
• 25 days paid annual leave + an extra celebration day for a special moment
• Discretionary bonus scheme
• Private medical care scheme
• Flexible benefits allowance - which you can choose to take as extra cash, or use towards other benefits
• Opportunity for personalised learning and in-the-moment experiences that enable you to thrive and excel in your role

We're ASOS. We blend our flair for fashion with our love of cutting- edge technology, but more importantly were interested in how we can bring the best out of you.

We exist to give people the confidence to be whoever they want to be, and that goes for our people too. At ASOS, you're free to be your true self without judgment, and channel your creativity into a platform used by millions.

Through our Fashion with Integrity strategy we are driving diversity, equity and inclusion across every aspect of ASOS and ensuring every ASOSer can be their authentic self at work. We want our people to be whoever they want to be, because we believe people who bring their best selves to work, do their best work.