Lead / Senior Full Stack Software Engineer (Shopify)

We’re looking for a Lead/Senior Full Stack Software Engineer who can architect and build solutions that push Shopify to its absolute limits. You won’t just be writing code; you’ll be defining our technical approach, taking ownership of our processes, and ensuring we deliver reliable, scalable, and maintainable systems.

Reporting directly to the Head of Technology, you’ll work within multidisciplinary teams across multiple high-stakes projects. This isn’t a role for someone who just wants to pick up tickets in isolation. We need a technical leader who operates at a high professional standard-not only in their coding ability, but in how they communicate complex technical solutions to the rest of the business.

How We Work

We deliver projects through four phases: Discover, Define, Deliver, and Deploy. This framework gives structure to complex work while keeping us focused on outcomes at every stage.

But here’s the thing - this process isn’t set in stone. The whole team contributes to how we work, and we’re always refining our approach. As a Lead/Senior Engineer, you will be central to defining, refining, and communicating our core development processes and best practices across the agency.

Location

We’re based in Leeds with a hybrid approach. Most of the team are in the office two to three days a week, with the flexibility to work remotely the rest of the time. We value face-to-face collaboration for the moments that matter, without requiring everyone to commute daily.

What You’ll Do

The work of your team can be broadly broken down into three core areas: creating reliable and scalable codebases, translating system designs into actionable implementation strategies, and owning Onstate’s development processes.

Day-to-day, you’ll be driving the technical delivery of projects while keeping a close eye on our 2026 Onstate Strategy. To do this, you will:

• Design & Develop: Create robust technology solutions and maintainable codebases. Take complex scope, convert it into clear technical briefs, and generate comprehensive project documentation.
• Innovate & Educate: Champion new technologies and standards. Educate yourself and your team on bleeding-edge tech, ensuring we are always working as efficiently and innovatively as possible.
• Collaborate Cross-Functionally: Interacting with and helping to organise the wider team is vital to your success. You will directly support:
• Project Management: Manage team sprint burndowns, communicate budget impacts, and refine project scope alongside the PMs.
• Design: Provide constructive feedback on UI/UX, inspire the team with suggested innovations, and guide designs safely around Shopify’s technical limitations.
• Data & Insight: Champion user value at every stage. You’ll have strong opinions on what data we need to collect, how we collect it, and why it matters.

• Strong knowledge of Shopify: You know its capabilities, its quirks, and how to build custom workarounds when it hits its limits.
• 5+ Years experience in JavaScript: You know the ecosystem inside out.
• Strong knowledge of NodeJS & Vanilla JavaScript (ES6+): You don’t just rely on frameworks; you understand the core language.
• Serverless technology: Experience building and deploying cloud functions.

Good-to-have skills:

• Experience with AI tools - when/where to use effectively.
• Experience with cloud platforms (AWS / GCP / Azure).
• Experience working with enterprise CMS platforms (e.g., Drupal, Umbraco).
• A solid understanding of User Stories and agile workflows.
• Experience with Test Automation, TDD, or BDD.

What Matters to Us

Beyond the tech stack, we want someone who genuinely cares about outcomes over outputs. Someone who asks “why” before diving into “how”. Someone who sees code as a tool to solve complex business problems, deliver incredible user experiences, and empower the wider team to do their best work.

If you’re excited by complex problems and want to work with a team that doesn’t shy away from difficult builds, we’d love to hear from you.

Pulled from the full job description

• Company pension
• Work from home
• Company events
• On-site parking

About Onstate

We’re a specialist Shopify agency that thrives on complexity. While others stick to standard builds, we take on the projects that make developers sweat - intricate customisations, challenging integrations, and solutions that push the platform to its limits. If it’s tough, we’re interested.

We build large, complex Shopify stores - product catalogues exceeding 8 million SKUs with daily price changes, custom systems that extend the platform far beyond its out-of-the-box capabilities, and highly personalised journeys where customers can design and visualise products they create themselves. We handle the scale and complexity most agencies wouldn’t touch.