Senior Software Engineer (React)

Cornerstone VC; City Of London; Hybrid; GBP 125,000 - 150,000; Full time

Job summary

A leading technology firm in London is looking for a Senior Engineer to shape the front-end architecture. You will design sophisticated React applications and mentor other team members. Ideal candidates should have over 4 years of experience with strong skills in React and Microsoft integrations. This hybrid role offers competitive salary and generous perks.

Benefits

Competitive salary & annual bonus

Equity in the company

Quarterly team socials & annual company offsite

Hybrid working options

25 days holiday + bank holidays

Annual learning & development budget

Private healthcare

Enhanced parental leave

Cycle to Work and other additional perks

Qualifications

• 4+ years of hands-on experience building production React applications.
• Strong proficiency in React, TypeScript, JavaScript, HTML, CSS, and modern web technologies.
• Experience integrating with Microsoft Office, especially Office.js and Word add-ins.

Responsibilities

• Design and build sophisticated React applications integrating with Microsoft Word, M365, and other Office products.
• Write clean, scalable, and maintainable code while driving performance and reliability.
• Collaborate with product, design, and engineering teams to deliver user-focused features.

Skills

React

TypeScript

JavaScript

HTML

CSS

Microsoft Office integration

Git

Performance optimisation

Job description

Location

London

Employment Type

Full time

Location Type

Hybrid

Department

Technology

About the role

We’re looking for a Senior Engineer with strong technical depth and a passion for building exceptional user experiences. You’ll play a key role in shaping our front-end architecture, collaborating closely with product and design teams, and delivering scalable, performant solutions used by legal professionals worldwide.

As a senior member of the team, you’ll act as a technical expert and a trusted partner helping to guide best practices, influence decisions, and mentor others through collaboration and example.

What you’ll do

• Design and build sophisticated React applications integrating with Microsoft Word, M365, and other Office products using Office.js.
• Write clean, scalable, and maintainable code while driving performance and reliability.
• Collaborate with product, design, and engineering teams to deliver user-focused, accessible features.
• Contribute to architectural discussions and help shape the evolution of our tech stack.
• Mentor and support team members through knowledge sharing, code reviews, and best practice guidance.
• Troubleshoot complex technical challenges and drive continuous improvement through automation and AI-assisted workflows.
• Maintain high-quality standards with robust testing, documentation, and security practices.

What you’ll bring

• 4+ years of hands-on experience building production React applications.
• Strong proficiency in React, TypeScript, JavaScript, HTML, CSS, and modern web technologies.
• Experience integrating with Microsoft Office, especially Office.js and Word add-ins.
• Familiarity with agentic coding assistants such as Claude Code or similar AI tools.
• Excellent communication and collaboration skills in English.
• Proven ability to work independently while contributing effectively to team goals.
• Experience working successfully in hybrid or remote development environments.
• Solid understanding of React performance optimisation (e.g. memoisation, code splitting, avoiding unnecessary re-renders).
• Experience with Git, version control best practices, and CI/CD pipelines.

We’ll be lucky if you have

• Knowledge of Microsoft Office Add-in guidelines and Office Store submission processes.
• Experience optimising in-browser text editors for speed and responsiveness.
• Prior experience in product-focused or startup environments.
• Exposure to AI-powered developer tools and automation workflows.

What we offer

• 💰 Competitive salary & annual bonus
• 📈 Equity in Definely
• 🎉 Quarterly team socials & annual company offsite
• 🏠 Hybrid working (Tues & Thurs in-office) + 1 month “work from anywhere”
• 🏖️ 25 days holiday + bank holidays
• 📚 £750 annual learning & development budget
• 🩺 Private healthcare (incl. dental & optical)
• 👶 Enhanced parental leave
• 🚲 Additional perks: Cycle to Work, Workplace Nursery salary sacrifice scheme, and top-quality equipment

Data Privacy Notice

By submitting your application, you agree that Definely may collect, process, and store your personal data as part of our recruitment process. We will use the information you provide to assess your qualifications for the role you are applying for and to communicate with you regarding your application. Your personal data will be stored for up to 12 months, after which it will be securely deleted unless we have another lawful basis to retain it. You have the right to access, correct, or request the deletion of your data at any time. For more details on how we handle your personal data and your rights, please email [e-mail] and we will send you our privacy policy.

If you have any concerns about how your data is being processed, please do not hesitate to contact us.