Senior Full Stack Engineer Contractor

OnBuy, part of the fast-growing OnCommerce family of marketplaces, is looking for a Senior Full Stack Engineer Contractor to take end-to-end ownership of features across a high-traffic ecommerce platform. This is a UK-based remote contract role for an engineer who thrives on ownership, pace, and building things that ship.

About the Role

As a Senior Full Stack Engineer Contractor at OnBuy, you will design, build, and maintain complete solutions spanning user interfaces, APIs, and backend systems. You will turn product requirements, designs, and wireframes into scalable, production-ready software, owning each feature from initial concept through development, testing, release, and ongoing monitoring. You will work across both monolith and microservices architectures while modernising and evolving existing systems.

Key Responsibilities

• Deliver full-stack features end to end, taking ownership from idea through to production and monitoring.
• Develop responsive, high-performance interfaces with modern JavaScript frameworks, translating UI/UX designs into clean, maintainable code.
• Architect and build scalable services and RESTful APIs across Laravel/PHP monolith and microservices environments.
• Maintain and gradually modernise legacy systems alongside new, scalable architecture.
• Embed quality throughout delivery by writing and maintaining unit, integration, and end-to-end automated tests.
• Lead and contribute to code reviews, debug issues across the stack, and uphold strong engineering standards.
• Tune systems for performance, reliability, and scale while working with large datasets in MySQL, NoSQL, and search platforms.
• Collaborate with Product, Design, QA, and fellow engineers, mentor junior team members, and explain technical concepts to non-technical stakeholders.

Qualifications

• Extensive full-stack experience with proven ownership of end-to-end delivery.
• Strong backend expertise in PHP and the Laravel framework.
• Advanced JavaScript (ES6+) skills with a modern framework such as React, Vue, or Angular.
• Hands-on experience designing RESTful APIs and scalable, well-architected systems.
• Working knowledge of MySQL alongside NoSQL databases such as Couchbase or MongoDB.
• Solid grasp of system architecture, microservices, and event-driven systems like RabbitMQ or Pub/Sub.
• Experience with cloud environments (GCP), Docker, and CI/CD pipelines.
• Desirable: a background in ecommerce or marketplace platforms and exposure to search platforms such as Constructor and Solr.

About OnBuy

OnBuy is the only marketplace in the world to offer customers instant Cashback on everything, and sits within OnCommerce, a global selling platform powering a growing network of retail brands. OnCommerce moves quickly, launches new ventures often, and gives its people genuine influence with no rigid corporate red tape. If you enjoy taking ownership and solving problems as you build, you will fit right in.

How to Apply

To apply, complete your application directly on this page, or you'll be redirected to the employer's application platform to finish submitting there.