Senior Fullstack Software Engineer

Firstup; Greater London; Hybrid; GBP 100,000 - 140,000; Full time

Benefits offered by this job

Health insurance

Flexible work hours

Job summary

Firstup in London is seeking a Senior Full Stack Software Engineer to design and deliver large-scale, multi-tenant cloud services with a focus on availability, reliability, and elegant architecture.

You will own end-to-end development across frontend, backend, and data layers, write production-grade code, and mentor engineers to elevate quality while collaborating with Product and Design.

Qualifications

• Bachelor’s degree in Computer Science or related field, or equivalent experience.
• 8+ years building reliable, performant applications and microservices in production environments.
• Proven full-stack experience across frontend (React.js), backend, and database layers.
• Contribute to production health, including on-call rotations and incident response.
• Technical depth in at least one domain: distributed systems, multi-tenant SaaS, databases, networking, security, serverless, or similar.
• Drive to build beautiful, intuitive products with the customer in focus; strong collaboration skills.

Responsibilities

• Build and own scalable SaaS applications end-to-end – frontend, backend, and data layers.
• Write production-grade code that is reliable, readable, efficient, and testable.
• Conduct thoughtful code reviews and maintain comprehensive documentation.
• Design future-ready architectures and proactively close gaps.
• Drive system availability and performance; investigate and resolve reliability issues.
• Champion shift-left testing and quality across the lifecycle.
• Leverage AI-assisted tools to accelerate development while ensuring code correctness.
• Lead by example, mentor engineers, and elevate engineering quality.
• Collaborate with Product & Design to translate requirements into intuitive UI.
• Promote engineering standards and solve high-impact problems.

Skills

Full stack fluency

React.js

TypeScript

Node.js

Go

Ruby on Rails

Education

Bachelor’s degree in Computer Science or related field

Job description

Senior Fullstack Software Engineer Overview

Company Name: Firstup

Job Role: Senior Fullstack Software Engineer

Qualifications: Not specified

Category: I

Job Type: Full Time

Location: Hybrid- London, UK

What we're looking for

• Bachelor’s degree in Computer Science or related field, or equivalent experience.

• 8+ years building reliable, performant applications and microservices in production environments. Proven full stack fluency – you’re comfortable across frontend, backend, and the database layer.

• Proven full-stack experience across frontend (React.js), backend, and database layers.

• Contribute to production health, including on-call rotations and incident response, in a “you build it, you run it” environment.

• Technical depth in at least one engineering domain: distributed systems, multi-tenant SaaS, application databases, networking, security, serverless, event streaming, or similar.

• A genuine drive to build beautiful, intuitive products with the customer always in focus. Innate curiosity — you love learning and have a desire to teach and lift others. Strong communication skills and openness to collaborative idea-sharing across teams.

Nice to have

• A polyglot mindset — you evolve with the tech. Familiarity with Ruby on Rails, TypeScript, Node.js , Go, or React.js is a strong plus.

• Core Stack Experience: Familiarity with Ruby (including Ruby on Rails), TypeScript, Node.js, Go, or React.js is a strong plus.

The role

We’re looking for a Senior Full Stack Engineer who thrives at the intersection of craft and scale. You’ll design and deliver large-scale, multi-tenant cloud services – with a relentless focus on availability, fault-tolerance, and elegant architecture. You’ll set the bar for engineering quality and help elevate those around you.

What you'll do

• Core Engineering & Ownership: Build and own scalable SaaS applications end-to-end – frontend, backend, and data layers. Write production-grade code that is reliable, readable, efficient, and testable. Raise the bar through thoughtful code reviews and comprehensive documentation.

• System Architecture: Design future-ready architectures and proactively close gaps before they become problems.

• Performance & Reliability: Drive system availability and performance – investigate, analyze, and resolve reliability issues across the stack. Recognize opportunities and advocate for better performance and efficiency of software, systems, and processes across teams.

• Shift Left Testing & Quality: You champion a rigorous ‘shift-left’ quality culture, embedding comprehensive testing-unit, integration, and contract-early and continuously in the development lifecycle, not as an afterthought.

• AI Integration: Leverage and advocate for AI-assisted tools (e.g., GitHub Copilot, Claude) to accelerate development while maintaining rigorous engineering judgment and accountability for code correctness.

• Leadership: Drive team-wide best practices, conduct quality code reviews, and mentor engineers to elevate overall engineering quality.

• Collaboration (Product & Design): Partner with Product and Design to translate requirements into intuitive UI, making informed technical trade-offs in the face of ambiguity.

• Collaboration (Engineering Standards): Champion engineering best practices across teams and collaborate on solving complex, high-impact problems.

Why Firstup?

Because you care – about people, the work you do, and the connections you make. Work is such a large part of life; it only makes sense to make it awesome.

If you want to engage brilliant minds in a high-growth and inclusive environment where ideas are rewarded regardless of who they come from, join us. This is a rapidly changing space so if you thrive on ambiguity, are hungry for a challenge, and have the guts to speak your mind, you could be a perfect fit.

We offer an excellent PTO program, great health benefits, a casual and friendly environment, remote work, and a leadership team who truly believes in your growth – both personally and professionally.

Firstup is committed to providing equal employment opportunities to all applicants for employment and to all employees, without regard to race, color, religion, gender, sexual orientation, gender identity or expression, national origin, age, protected disability, veteran status or any other protected status in accordance with applicable federal, state or local laws.

Visa sponsorship: check with employer