Fullstack Software Engineer

Location: London, UKOn-Site | Full-timeCompensation: Competitive CompensationOur client is an early-stage, high-impact, revenue-generating AI startup that is fundamentally redefining business automation. While most applied AI companies focus on selling software tools, this organization sells completed business outcomes—delivering highly automated, autonomous pipelines that directly close revenue for clients ranging from fast-growing startups to Fortune 500 enterprises.With strong product-market fit, consistent month-over-month growth, and a clear roadmap, the engineering team is currently scaling up. This is a rare opportunity to join an elite, tight-knit, and highly leveraged engineering team where every line of code directly drives revenue and shapes foundational systems from scratch.The team operates in a fast-paced, high-momentum environment that values intense collaboration. To maintain this high-engagement culture, this role is 100% on-site (five days a week) at the client's office in Piccadilly, London.Key ResponsibilitiesEnd-to-End System Ownership: Own complex technical problems from scope to deployment, building and iterating on foundational systems from scratch with real users from day oneNext-Generation Infrastructure: Build and scale custom calling and dialer infrastructure with autonomous AI agents at the coreAutonomous AI Workflows: Develop and optimize high-throughput AI Inbound SDR systems capable of autonomously managing thousands of callbacks and converting them to scheduled meetingsClosed-Loop Intelligence: Build post-interaction intelligence layers that generate real-time insights, customized proposals, and targeting signals to feed directly back into campaignsHigh-Scale Data Pipelines: Engineer advanced prospecting engines featuring custom web scraping, AI-driven qualification pipelines, and highly optimized list-logic systemsStack Optimization: Work within a modern, robust tech stack utilizing TypeScript, React, Next.js, AWS, OpenSearch, Trigger.dev, ClickHouse, and DatadogRequirementsExperience & Background Top-Tier Tech Experience: Proven software engineering experience at a globally recognized, high-caliber technology organization (e.g., FAANG, Bloomberg, Stripe, Shopify, Revolut, Datadog, or direct equivalent) is strictly requiredStartup DNA: Prior experience working in a fast-growing startup or highly agile team (<20 people, such as YC-backed companies), demonstrating a track record of wearing multiple hats and shipping high-impact codeProfessional Tenure: Minimum of 3+ years of professional software engineering experience for mid-level candidates, and 6+ years for senior-level candidatesTechnical & Academic QualificationsFull-Stack Proficiency: Deep expertise in full-stack web development, with strong production experience in TypeScript and React (Next.js experience is highly preferred)CS Fundamentals: Exceptional computer science fundamentals, including data structures, algorithms, and performance trade-offs, backed by a Computer Science degree or equivalent from a top-tier universityArchitectural Capability: Proven ability to design complete, end-to-end systems from scratch, demonstrating true systems-level thinking rather than simply executing on pre-defined architecturesAI & LLM Tooling: Practical experience building with AI/LLMs, autonomous agents, RAG systems, or advanced LLM-powered application featuresLocation & CommitmentOn-Site Presence: Must be currently based in London (or fully willing to relocate) and committed to working on-site five days a week in Piccadilly (no exceptions)BenefitsCompetitive Compensation: Market-aligned base salary with highly flexible stock-for-salary trade-off options, structured to reward those who value meaningful equity in a high-growth, revenue-generating startupVisa Sponsorship: Full visa sponsorship is available for qualified international candidatesHealth & Wellness: Comprehensive private health and dental insuranceRetirement: Company-matched pension schemeOffice Perks: Fully covered late-night dinners and taxi rides home for team members working past 8:00 PMInterview ProcessOur client running this search utilizes a rigorous, two-stage technical evaluation designed to identify exceptional systems thinkers.Stage 1: Screening CallAn introductory conversation to align on professional background, career aspirations, and cultural fitStage 2: Technical Evaluation PhaseSystems Design Interview: An interactive session focused on mapping a complex, real-world problem statement to a highly scalable, end-to-end architectural solutionTake-Home Assessment: A practical exercise utilizing a provided application scaffold. Candidates will solve a problem using an AI agent and must be prepared to articulate, explain, and defend the agent's outputsStage 3: Follow-Up & Culture FitA final discussion to meet additional team members, review role expectations, and finalize compensation detailsDue to the high volume of applications we anticipate, we regret that we are unable to provide individual feedback to all candidates. If you do not hear back from us within 4 weeks of your application, please assume that you have not been successful on this occasion. We genuinely appreciate your interest and wish you the best in your job search.Commitment to Equality and Accessibility:At MLabs, we are committed to offer equal opportunities to all candidates. We ensure no discrimination, accessible job adverts, and providing information in accessible formats. Our goal is to foster a diverse, inclusive workplace with equal opportunities for all. If you need any reasonable adjustments during any part of the hiring process or you would like to see the job-advert in an accessible format please let us know at the earliest opportunity by emailing human-resources@mlabs.city.MLabs Ltd collects and processes the personal information you provide such as your contact details, work history, resume, and other relevant data for recruitment purposes only. This information is managed securely in accordance with MLabs Ltd's Privacy Policy and Information Security Policy, and in compliance with applicable data protection laws. Your data may be shared only with clients and trusted partners where necessary for recruitment purposes. You may request the deletion of your data or withdraw your consent at any time by contacting legal@mlabs.city.