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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. Salary £80-110k + Bens + Stock

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 / event-driven 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!

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