Senior Full Stack Engineer

Senior Full Stack Developer

Reporting to: Engineering Manager

Office Environment: Hybrid (minimum two days per week)

Type: Full time, permanent

Join Our Mission

Skip the queue. Shape the future. See real impact.

At QuantSpark, we’re transforming how data and AI serve society. We combine the analytical discipline of strategy consulting with the pace and ownership of a scale-up. That means you’ll work directly on the problems that matter most; whether combating economic crime, modernising government services, or accelerating commercial growth for FTSE 100 companies.

Here, you’ll compress 5–10 years of traditional career progression into 2–3 years. From day one, you’ll lead end-to-end projects, access leadership directly (including the CEO), and build cross-industry expertise that usually takes a decade to gain.

We don’t just develop—we build, own, and scale solutions that shape the organisations we work with and have meaningful societal impact.

Our Client Portfolio

We partner with forward-thinking organisations across sectors:

• Private Equity & Financial Services: Portfolio analytics, AI-powered value creation, and risk management tools for global investment and wealth firms.
• Retail & Consumer: Pricing optimisation, inventory efficiency, and personalised engagement for major UK retailers and brands.
• Asset Management: Advanced investment platforms and automated risk management for asset managers.
• Public Sector: Trusted by multiple UK government departments for fraud analytics, predictive maintenance, and supply chain optimisation.
• SaaS & Manufacturing: Sector-spanning technology transformation for SaaS innovators and manufacturers.

The Role

You'll design, build, and scale web applications across backend and frontend, owning projects from ideation through to production — architecture, CI/CD, cloud infrastructure, monitoring, the lot.

We're a small team that punches well above its weight. Client feedback is outstanding, and every engineer here has a visible impact.

Day to day, you'll:

• Architect and deliver scalable, secure software for commercial clients across multiple sectors.
• Assess technical trade-offs and guide design decisions across projects.
• Write, review, and own high-quality code — primarily Python (Flask, FastAPI, or Django) and JavaScript/TypeScript (React preferred).
• Build and maintain RESTful APIs and modern frontends.
• Work directly with clients — communicating clearly, understanding the why behind what you're building.
• Feed into new client proposals and help improve internal engineering processes.
• Mentor junior developers through code reviews, pairing, and knowledge-sharing.
• Use AI coding agents to accelerate delivery whilst maintaining correctness and security.

AI Engineering (Required)

• Hands-on experience with AI coding agents in day-to-day work — prompting, iterating, reviewing generated code, validating outputs.
• Working understanding of LLM fundamentals and limitations (hallucinations, context windows, evaluation).
• Familiarity with prompting patterns, tool use, and concepts like RAG and embeddings.
• Awareness of safety and privacy concerns when using AI tools (secrets, PII, licensing).
• Ability to integrate AI into your workflow without compromising code quality.

What We're Looking For...

• 5+ years' experience as a full-stack engineer.
• Strong track record delivering enterprise-grade web applications and APIs.I Want to Work for a Company That…

What We Offer

• Tech ownership and autonomy from day one.
• High-impact work — you'll see real results within months, not years.
• Room to innovate, not just maintain.
• A small, collaborative team that owns problems end to end and learns fast.
• Clients ambitious enough to rethink how they use data and technology.
• A clear path to leading technical programmes and shaping strategy. Growth here is earned, not queued.

Perks & Benefits

• £6,000 annual training & conference budget to stay at the cutting edge
• Up to 6% matched pension for long-term financial security
• Comprehensive private healthcare via Vitality
• EMI share options scheme—own a piece of the growth you help create
• Work from anywhere in the world for up to 1 month/year
• 25 days holiday + buy/sell up to 5 additional days
• Cycle-to-work scheme for sustainable commuting
• Central London office stocked with refreshments, socials, and vibrant atmosphere
• Exclusive discounts on retail, travel, tech & fitness memberships
• Access to cutting-edge tools, platforms, and regular tech talks & innovation time

Equal Opportunities

We're building a team that benefits from different perspectives, experiences, and ways of thinking. We know that great talent comes from all backgrounds, and we encourage applications from everyone who meets the role requirements, regardless of age, disability, gender identity, race, religion, sexuality, or any other characteristic. If you're unsure whether you're a perfect fit but believe you can do the job well, we'd still like to hear from you. We hire based on your skills, potential, and ability to contribute to our team, and we're committed to a fair and objective selection process for all candidates.