Senior Full Stack Software Engineer

Position Description At CGI, you’ll help create intuitive, high-value software solutions that make complex technology and data easier to use, enabling our clients to achieve better outcomes with less dependency on specialist resources. As a Senior Full Stack Software Engineer, you’ll combine creative thinking with hands-on engineering to shape user-focused applications across modern frontend and backend technologies. You’ll have the ownership to influence technical approaches, solve meaningful challenges and turn ideas into robust solutions, while collaborating with experienced CGI Partners who will support your development. This is an opportunity to make a tangible impact on an important programme, contribute ideas that improve how solutions are delivered, and continue growing your expertise within one of the world’s largest IT and business consulting services organisations. CGI was recognised in the Sunday Times Best Places to Work List 2025 and has been named a UK ‘Best Employer’ by the Financial Times. We offer a competitive salary, excellent pension, private healthcare, plus a share scheme (3.5% + 3.5% matching) which makes you a CGI Partner not just an employee. We are committed to inclusivity, building a genuinely diverse community of tech talent and inspiring everyone to pursue careers in our sector, including our Armed Forces, and are proud to hold a Gold Award in recognition of our support of the Armed Forces Corporate Covenant. Join us and you’ll be part of an open, friendly community of experts. We’ll train and support you in taking your career wherever you want it to go. Due to the secure nature of the programme, you will need to hold UK Security Clearance or be eligible to go through this clearance. This is an office based role. Your future duties and responsibilities In this role, you will design, develop and enhance modern software applications that simplify complex processes and deliver an intuitive experience for users. Working across the technology stack, you will use React alongside Python and FastAPI to build reliable, scalable solutions, taking ownership of your work from design through to delivery. You will collaborate with engineering, data and infrastructure specialists to solve technical challenges and identify opportunities to improve the way our solutions are built and operated. You’ll have the freedom to bring forward new ideas, while benefiting from the knowledge and support of an experienced CGI community committed to delivering high-quality outcomes. Design & Deliver: Build high-quality frontend and backend software using React, Python and FastAPI. Own & Improve: Take responsibility for solutions throughout the development lifecycle and continually improve their quality, reliability and usability. Integrate & Connect: Develop and maintain REST APIs and secure integrations using appropriate authentication methods. Test & Assure: Create robust automated tests using tools such as Pytest and VCR to maintain software quality. Optimise & Scale: Use technologies including Redis, RabbitMQ and Celery to support efficient, resilient applications. Containerise & Deploy: Develop solutions for modern containerised environments using Docker and Kubernetes. Collaborate & Create: Work with multidisciplinary teams to turn complex requirements into straightforward, user-focused solutions. Automate & Enhance: Contribute to effective development and delivery practices using GitLab, Concourse and modern Python tooling. Required Qualifications To Be Successful In This Role You should bring strong software engineering experience and be comfortable contributing across modern application architectures. You will have proven Python backend development expertise and/or strong React frontend experience, together with an engineering mindset focused on maintainability, testing and continuous improvement. You should enjoy taking ownership of technical challenges while collaborating with colleagues and sharing expertise across the team. Strong commercial software engineering experience using Python and/or React. Strong proficiency in Python 3 and experience developing APIs with FastAPI/Uvicorn for backend-focused positions. Experience building modern, accessible and intuitive user interfaces with React for frontend-focused positions. Good understanding of REST APIs, HTTP and authentication, including technologies such as JWTs and certificates. Experience with relevant Python technologies such as Pydantic, NumPy, Jinja2 and virtual environments. Proven ability to create automated tests using Pytest and API testing approaches such as VCR. Experience with, or a good understanding of, technologies such as RabbitMQ, Redis and Celery. Knowledge of containerised application development using Docker and Kubernetes. Experience working with source control and delivery tooling such as GitLab and Concourse. Ability to collaborate effectively, contribute new ideas and take ownership of delivering high-quality technical outcomes. Together, as owners, let’s turn meaningful insights into action. Life at CGI is rooted in ownership, teamwork, respect and belonging. Here, you’ll reach your full potential because… You are invited to be an owner from day 1 as we work together to bring our Dream to life. That’s why we call ourselves CGI Partners rather than employees. We benefit from our collective success and actively shape our company’s strategy and direction. Your work creates value. You’ll develop innovative solutions and build relationships with teammates and clients while accessing global capabilities to scale your ideas, embrace new opportunities, and benefit from expansive industry and technology expertise. You’ll shape your career by joining a company built to grow and last. You’ll be supported by leaders who care about your health and well-being and provide you with opportunities to deepen your skills and broaden your horizons. That same commitment to fairness extends to how we use technology. To support our recruitment team, AI tools may be used to help assess applications though they never replace human judgement. All hiring decisions remain entirely in the hands of our recruitment professionals. Come join our team—one of the largest IT and business consulting services firms in the world.