Senior/Principal Full Stack Software Engineer

ZipRecruiter; City Of London; Hybrid; GBP 150,000 - 200,000; Full time

Job summary

A fast-growing B2B SaaS company is seeking a Senior or Principal Full-Stack Software Engineer to lay the technical foundation of their platform. This high-impact role emphasizes collaboration across teams, architecture design, and scaling infrastructure. Benefits include a competitive salary, share options, and flexible working arrangements. UK right to work is required.

Benefits

Competitive salary

25 days holiday + bank holidays

Share options

Private healthcare

Flexible working arrangements

Strong career development

Qualifications

• 5+ years of experience as a full-stack engineer.
• Experience in early-stage startups and B2B SaaS is preferred.
• Strong proficiency in modern front-end frameworks like React.

Responsibilities

• Design and implement scalable and secure systems.
• Own core parts of the platform architecture.
• Collaborate with cross-functional teams on technical delivery.

Skills

JavaScript/TypeScript

React

Backend architecture

Collaboration and communication

SQL and NoSQL databases

Project leadership

Tools

AWS

Azure

GCP

Job description

Overview

We are currently working with an ambitious and well-funded early-stage B2B SaaS company that’s building something genuinely transformative in their category. As they enter a critical phase of growth, they’re looking to hire a Senior or Principal Full-Stack Software Engineer to help lay the technical foundations of their platform and influence both the engineering direction and long-term product strategy.

This is a high-impact role offering direct collaboration with cross-functional teams, including senior leadership and the CEO. The successful candidate will play a key part in shaping architecture, scaling infrastructure, and delivering features that add real value to users.

Responsibilities

• Design and implement scalable, secure, and high-performance systems.
• Own and evolve core parts of the platform architecture.
• Collaborate with product, commercial, and leadership teams to align technical delivery with strategic goals.
• Write clean, maintainable code across the full stack and contribute to reviews and debugging.
• Bring new ideas and best practices to continuously elevate engineering standards.

Ideal Experience

• 5+ years of experience working with JavaScript/TypeScript as a full-stack engineer.
• Experience leading projects or teams in a technical capacity.
• Previous exposure to early-stage startups, ideally in B2B SaaS.
• Strong proficiency in modern front-end frameworks (particularly React).
• Experience designing and integrating REST or GraphQL APIs (bonus if you’ve built SDKs or documentation).
• Solid understanding of SQL and NoSQL databases and backend architecture.
• Familiarity with cloud platforms such as AWS, Azure, or GCP.
• A pragmatic, product-first mindset—someone who values simple solutions and rapid iteration.
• Strong collaboration and communication skills.

What’s on offer?

• Competitive salary
• 25 days holiday + bank holidays
• Share options in a fast-growing business
• Private healthcare (including dental and optical)
• Flexible working (remote or hybrid – dog-friendly office in London available)
• Strong career development and influence in a key hire

PLEASE NOTE

• UK right to work required – unfortunately, visa sponsorship isn’t available.
• The team is passionate about building an environment where everyone can thrive and do their best work.

If you're a hands on engineer excited by the idea of helping build a product from the ground up and want to join a team that values innovation, ownership, and velocity we would love to hear from you.