Our client, a mission-led consultancy, is looking for an experienced Principal Software Engineer (Python or Java) to join their growing team. They deliver secure, modern software solutions to the UK Government and Defence sectors, enabling clients to build scalable systems and progressive web applications that drive real impact. This is a senior-level opportunity for a hands-on engineer who enjoys leading by example, thrives in agile environments, and is passionate about shaping engineering best practice while still contributing to the codebase. Key Responsibilities Lead the design, development, and testing of secure, scalable systems using Python or Java with modern front-end frameworks (e.g., React) Architect and maintain APIs, data pipelines, and cloud-native solutions (AWS, Azure, private cloud) Drive adoption of DevOps practices CI/CD, containers, infrastructure-as-code Guide and mentor engineers, promoting best practice, clean coding, and agile delivery Collaborate with stakeholders and clients to shape technical direction and ensure robust, user-focused solutions Contribute across the full software development lifecycle, from discovery to production support Essential Skills & Experience Deep expertise in Python or Java, with strong full-stack engineering skills Proven experience leading teams or projects at a senior/principal level Strong knowledge of system architecture, cloud solutions, and API design Familiarity with DevOps tools and automation (CI/CD, containers, IaC) Track record of delivering secure, production-grade systems in agile teams Excellent stakeholder engagement, influencing, and communication skills Desirable Background in secure or classified environments Knowledge of ITSM or systems within the government/defence sector Experience balancing technical leadership with hands-on development Whats in It for You Flexible working 37.5 hrs/week with remote and hybrid options Learning & development budget for training, certifications, and conferences Private healthcare & matched pension scheme Monthly socials and quarterly company meetups Clear career progression into leadership roles in a high-impact sector Diversity & Inclusion Our client is an equal opportunities employer and a Disability Confident organisation, committed to fostering a workplace where diverse perspectives are celebrated and everyone can thrive. How to Apply If youre an experienced Principal Software Engineer with expertise in Python or Java, and youre excited to help deliver solutions that truly matter, wed love to hear from you.