Principal Software Engineer with strong Java, Spring Boot or Micronaut experience is required to join an early-stage green energy technology start-up building advanced SaaS and data platform products for the renewable energy sector. You’ll take a leading role in the design, architecture, delivery and support of a new microservices-based SaaS product, working across scalable distributed systems, cloud-native engineering, DevOps, Continuous Delivery, test automation and ideally some frontend development with React / MUI. This role will suit someone from a small, scale-up or product-focused SaaS software business who enjoys hands-on engineering, technical leadership and building resilient, maintainable software with real-world impact. The role is potentially remote, although candidates should be accessible to the central Cambridge office, which would be an advantage. Key skills required for the Principal Software Engineer Proven experience taking a leading role in the design, architecture, delivery and support of scalable software products. Strong experience building and operating Java-based applications in an enterprise environment. Strong experience with Spring Boot or Micronaut, ideally as microservices within a SaaS platform. Deep understanding of distributed systems, with strong opinions on resilience, scalability, maintainability and software quality. Experience shaping technical architecture and translating product requirements into pragmatic, well-structured technical designs. Ability to lead delivery of complex software features and services within a product-led, Continuous Delivery environment. Familiarity with container management solutions such as Kubernetes, ECS or similar, ideally within managed cloud platforms such as EKS, GKE or equivalent. Good understanding of DevOps practices, Continuous Delivery and modern cloud-native software delivery. Comfortable leading prototyping, feasibility studies and build / buy / partner recommendations for new product capabilities. Able to mentor, coach and upskill engineers through code reviews, pair programming, mob programming and technical guidance. Full stack awareness, with frontend development experience ideally using React / MUI or similar modern UI frameworks/component libraries. Experience working in a small, scale-up, start-up or product-focused SaaS software business. Any experience with Domain Driven Design, data engineering, data products, data pipelines, data mesh architectures, platform engineering, ML engineering, IoT hardware, embedded systems or firmware development would be advantageous. A genuine interest in renewable energy, climate technology or building software with meaningful impact. What you’ll do as a Principal Software Engineer Take a leading role in the design, delivery and support of green energy software as part of a product-led, Continuous Delivery lifecycle. Shape the architecture and technical direction of a rapidly evolving SaaS product. Build new Java-based services, APIs and product features in collaboration with the wider engineering team. Work with product stakeholders to translate customer and business requirements into robust technical designs. Lead prototyping and feasibility work for new capabilities, including input into build, buy or partner decisions. Act as a technical subject matter expert and point of contact for internal and external stakeholders. Guide engineering practices across scalability, reliability, automated testing, code quality and maintainability. Support and coach other engineers through code reviews, pairing, mob programming and direct technical mentoring. Participate in product demos, customer feedback sessions, retrospectives and continuous improvement discussions. Write appropriate test automation to support the reliability of services and product features. Help operate and support the services you build as part of a team-wide engineering approach. Contribute more broadly to company goals where your experience, technical judgement and enthusiasm can make an impact. Why this role? This is a chance to join a mission-led, early-stage technology business at a formative stage and play a major role in shaping both the product and engineering culture. You’ll work with a diverse team combining renewable energy domain expertise, modern software engineering and operational delivery experience. The environment is collaborative, product-focused and technically ambitious, giving you the opportunity to remain hands-on while influencing architecture, engineering standards and product direction. You’ll be building software that supports the transition towards a greener energy world, with scope to contribute across data engineering, data mesh, ML-enabled applications, cloud-native platforms, IoT and distributed systems as the product evolves. You do not need to tick every box. We are looking for a talented, pragmatic and enthusiastic Principal Software Engineer who wants to make a difference, lead by example and help build a high-quality engineering function. Opus Resourcing acts as an employment agency with respect to permanent employment. Apply now or message us for more details. Referrals always welcome! PrincipalEngineer JavaJobs SaaSJobs GreenTech ClimateTech