Senior Full-Stack Software Engineer – Generative AI @MarshTech

Company:Mercer

Description:

We are seeking an experienced Senior Full-Stack Engineer, Generative AI to design, build, and operate enterprise-grade AI-enabled solutions across our technology organization. This role is for a senior individual contributor who combines strong hands-on engineering skills with sound technical judgment and the ability to raise the quality of delivery within a team or domain.

You will work on complex, real-world problems, developing AI-enabled web applications across the full stack using modern frontend and backend technologies, Large Language Models (LLMs), and cloud infrastructure. You will play a key role in evolving solutions from early proof of concept through to scalable, production-ready systems used by internal and external stakeholders.

In this role, you are relied upon to ensure solutions meet enterprise standards for security, reliability, scalability, maintainability, and testability, and to help teams apply generative AI responsibly and effectively in production environments.

We will count on you to:

• Lead the technical design and delivery of complex, AI-enabled features or services.

• Design, build, and evolve full-stack applications using modern frontend and backend frameworks.

• Build and maintain robust, high-performance APIs using NestJS / NodeJS or FastAPI / Python.

• Integrate Large Language Model (LLM) capabilities into production systems, selecting appropriate patterns, tools, and architectures.

• Guide the evolution of proofs of concept into production-ready, scalable solutions within enterprise constraints.

• Own technical solutions end-to-end, including design, implementation, deployment, and operational readiness.

• Make sound engineering decisions that balance security, scalability, reliability, maintainability, and testability.

• Act as a hands-on engineer: write production code, review code, and contribute to testing and observability.

• Champion strong engineering practices, including code quality, testing, CI/CD, and documentation.

• Identify opportunities for reuse and contribute to shared components, patterns, and standards.

• Collaborate closely with product, architecture, security, and platform teams in an Agile delivery environment.

• Provide technical guidance and mentorship to other engineers through design discussions and example.

• Contribute to continuous improvement of engineering practices within the team or domain.

What you need to have: 

• 6+ years of professional software engineering experience, including building and operating production systems.

• 2+ years of hands-on experience working with Large Language Models (LLMs) in applied or production contexts.

• Strong proficiency in a modern frontend framework, ideally React with TypeScript.

• Deep hands-on experience with NodeJS / NestJS and/or Python (FastAPI or Django).

• Strong understanding of API design, distributed systems, and service-oriented architectures.

• Proven experience deploying, operating, and supporting systems in cloud environments.

• Experience working in Agile delivery teams and collaborating across disciplines.

• Strong communication skills, with the ability to explain technical concepts to a range of audiences.

• Sound engineering judgment and a pragmatic, delivery-focused mindset.

What makes you stand out

• Experience designing or implementing Retrieval-Augmented Generation (RAG) systems in applied or production contexts.

• Experience evaluating and selecting GenAI frameworks or tools (e.g., LangChain, LangGraph, LlamaIndex, CrewAI) based on problem context.

• Experience with AI agents, orchestration patterns, or workflow-based AI systems, including understanding when such approaches are appropriate.

• Familiarity with prompt engineering, evaluation techniques, and guardrails for LLM-based systems.

• Experience with cloud-native architectures, CI/CD pipelines, and infrastructure-as-code.

• Understanding of security-driven design and how to address common application or platform vulnerabilities in enterprise systems.

Why join our team:

• We help you be your best through professional development opportunities, interesting work and supportive leaders.

• We foster a vibrant and inclusive culture where you can work with talented colleagues to create new solutions and have impact for colleagues, clients and communities.

• Our scale enables us to provide a range of career opportunities, as well as benefits and rewards to enhance your well-being.

• An opportunity to work in a fast-growing, innovative company with lots of room for progression and career growth;

• A fail-friendly environment that encourages learning and initiative;

• A yearly budget and the opportunity to build your flexible benefits package (up to 20% of your annual salary);

• 30+ days off (25 legal days off , 1 extra day off on your birthday, public holiday replacement days, extra buy/sell from your benefits budget);

• Performance Bonus scheme

• Matching charity contributions, charity days off, and the Pay it Forward charity challenge;

• Core benefits - Pension, Life and Medical Insurance, Meal Vouchers, Travel Insurance;

• We champion flexible working, and our mission is to help you find YOUR work-life balance, whether that's standard working, flex-time working, or working from home

Marsh (NYSE: MRSH) is a global leader in risk, reinsurance and capital, people and investments, and management consulting, advising clients in 130 countries. With annual revenue of over $24 billion and more than 90,000 colleagues, Marsh helps build the confidence to thrive through the power of perspective. For more information, visit corporate.marsh.com, or follow us on LinkedIn and X.

Marsh is committed to creating a diverse, inclusive and flexible work environment. We aim to attract and retain the best people and embrace diversity of age, background, disability, ethnic origin, family duties, gender orientation or expression, marital status, nationality, parental status, personal or social status, political affiliation, race, religion and beliefs, sex/gender, sexual orientation or expression, skin color, or any other characteristic protected by applicable law.

Marsh is committed to hybrid work, which includes the flexibility of working remotely and the collaboration, connections and professional development benefits of working together in the office. All Marsh colleagues are expected to be in their local office or working onsite with clients at least three days per week. Office-based teams will identify at least one “anchor day” per week on which their full team will be together in person.