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.

We are a team of driven and motivated people who thrive when working  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.

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.

• 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

• 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

• 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

• 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

• Optimise systems for performance, reliability, and scale
• Work with large-scale data systems (MySQL, No
  
  SQL, search platforms)
• Identify bottlenecks and proactively improve system efficiency

• 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

• 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
• Experience with MySQL and No
  
  SQL databases (e.g. Couchbase, Mongo
  
  DB)
• Strong understanding of system architecture and microservices
• Experience with event-driven systems (e.g. Rabbit
  
  MQ, Pub/Sub) and cloud environments (GCP)
• Familiarity with Docker and CI/CD pipelines
• Strong engineering practices: testing, code quality, and production ownership

• Experience in eCommerce or marketplace platforms
• Cloud experience (GCP)
• Experience with No
  
  SQL (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.

• 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

UK remote or if you prefer coming into the office can be Hybrid if you live near our Manchester or Bournemouth's offices.

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.