Senior Full Stack Engineer

Who are OnBuy?

OnBuy are an online marketplace who are on a mission of being the best choice for every customer, everywhere.

We have recently been named one of the UK's fastest-growing tech companies in the Sunday Times 100 Tech list.

All achievements we are very proud of, but we don't let that go to our head. We are all laser focused on our mission and understand the huge joint effort ahead of us needed to succeed.

Working at OnBuy:

We are a team of driven and motivated people who thrive when working at pace. To succeed at OnBuy you need to take charge and fully own your responsibilities, rolling your sleeves up when needed to 'get it done'. Working at OnBuy you are surrounded by so much opportunity, but you must possess the ability to stay focused and prioritise ruthlessly. Most importantly, you will thrive in an ever-changing environment as we are constantly evolving.

At OnBuy, you're not just a number or another cog in a machine. We are creating something really special, and you have the opportunity to affect meaningful change and have your voice heard. We are a close team, who have the opportunity to learn and grow as OnBuy evolves.

About the Role

This is a critical role responsible for building, scaling, and evolving OnBuy’s core commerce platform across both front-end and back-end systems. As a Senior Full Stack Engineer, you will own engineering delivery end-to-end; from customer-facing experiences to underlying services and data systems. You will operate within a cross-functional team and be accountable for shipping high-quality, scalable solutions that directly impact GMV, seller performance, and customer experience. This role moves beyond “front-end vs back-end” you are an Engineer responsible for outcomes, not layers.

Key Responsibilities

End-to-End Engineering Ownership

• Design, build, and maintain full-stack solutions across UI, APIs, and backend systems
• Translate product requirements, designs, and wireframes into scalable, production-ready systems
• Own features from concept → development → testing → release → monitoring

Front-End Excellence

• Build responsive, high-performance user interfaces using modern JavaScript frameworks
• Translate UI/UX designs into clean, maintainable code
• Optimise applications for speed, scalability, and usability

Back-End & Platform Engineering

• Design and develop scalable services and APIs
• Work across monolith and microservices architecture (Laravel / PHP services)
• Maintain and evolve legacy systems while building modern, scalable architecture

Quality & Engineering Standards

• Own quality to production — testing is embedded, not a phase
• Write and maintain automated tests (unit, integration, end-to-end)
• Participate in and lead code reviews to ensure high engineering standards
• Debug, troubleshoot, and resolve issues across the stack

Performance & Scalability

• Optimise systems for performance, reliability, and scale
• Work with large-scale data systems (MySQL, NoSQL, search platforms)
• Identify bottlenecks and proactively improve system efficiency

Collaboration & Leadership

• Work in cross-functional teams with Product, Design, QA, and other Engineers
• Mentor and support less experienced engineers
• Communicate technical concepts clearly to non-technical stakeholders

Experience & SkillsEssential

• Strong full stack engineering experience, owning end-to-end delivery
• Proven backend expertise in PHP (Laravel)
• Strong JavaScript (ES6+) skills with modern frameworks (React/Vue/Angular)
• Experience designing and building RESTful APIs and scalable systems
• Strong understanding of system architecture and microservices
• Experience with MySQL and NoSQL databases (e.g. Couchbase, MongoDB)
• Experience with event-driven systems (e.g. RabbitMQ, Pub/Sub) and cloud environments (GCP)
• Familiarity with Docker and CI/CD pipelines
• Strong engineering practices: testing, code quality, and production ownership

Desirable

• Experience in eCommerce or marketplace platforms
• Cloud experience (GCP)
• Experience with NoSQL (e.g. Couchbase) and Search platforms (e.g. Constructor & Solr)
• Experience working in microservices architecture

The salary on offer for this role is £65000- £70000 depending on experience.

We also offer the following benefits:

• Company Equity- In return for helping us to grow, we’ll offer you company equity, meaning you own a piece of this business we are all working so hard to build.
• 25 days annual leave + Bank Holidays
• 1 extra day off for your Birthday
• Employee Assistance Programme
• Perks at Work benefit platform
• Opportunities for career development and progression

This role is UK remote or if you prefer coming into the office can be Hybrid if you live near our Manchester or Bournemouth's office spaces.Our Commitment

OnBuy is an equal opportunities employer. We are dedicated to creating a fair and transparent workforce, starting with a recruitment process that does not discriminate on the basis of gender, sexual orientation, marital or civil partnership status, pregnancy or maternity, gender reassignment, race, colour, nationality, ethnic or national origin, religion or belief, disability, or age.

Just a heads up — we never use WhatsApp. or any messaging apps to contact candidates

If someone reaches out this way, it isn’t us and let the recruitment team know.