Senior Software Engineer

About Belisar Belisar is the CRM designed for government contracting. It enables the best technology to win, fusing internal context, intuitive AI, and real-time data into a unified view of the market. Federal contracting has long run on tools that were never built for it: Generic CRMs designed for commercial sales, legacy data platforms that surface noise instead of signal, and institutional knowledge locked in spreadsheets and inboxes. Belisar unifies all the important intelligence into a single, AI-native platform — so teams can see opportunities earlier, move faster, and win the work that matters. Belisar is backed by a16z and trusted by leading defense, space, and government leaders including Boeing, Forterra, Scout AI, Vannevar Labs, Aevex, and the Defense Innovation Unit (DIU). Together, we're building toward one outcome: The best technology wins, and it reaches the missions that need it most. The Role We're looking for a full-stack software engineer to join a small, high-density engineering team building Belisar's platform from the ground up. This is a 0-to-1 role in the literal sense: most of what you ship this year doesn't exist yet. You'll own features end-to-end, working directly with our CEO, CTO, and founding engineers, sit close to real customers, and make architecture calls that are still running the platform a year from now, not decisions made for you by a platform team five layers up. What You’ll Do • Lead the design and development of complex, full-stack software systems, contributing hands-on across the stack. • Review code, maintain high engineering standards, and mentor engineers through technical guidance and feedback. Scope and design scalable system architectures, ensuring reliability, performance, and maintainability. • Collaborate cross-functionally with teams such as Sales, Mission Ops, and Marketing to align product delivery with customer and business needs. • Drive development workflows and release coordination, ensuring smooth deployments and high-quality production systems. • Contribute to building modern AI-enabled products, including backend services, workflows, and integrations with LLM-powered systems. • Help grow the engineering team by participating in hiring and technical interviews. What We're Looking For • Led teams building or personally built complex, distributed systems with real users and uptime requirements. • Demonstrated mastery in at least one of our core areas: • Backend/Data: APIs, ETL • Frontend: UI/UX • Search/Analytics: PostgreSQL, Elasticsearch, schema design, relevance tuning. • Designed resilient architectures: clear boundaries, smooth releases, and instrumentation that catches issues before users do. • Communicated clearly with both technical and non-technical stakeholders. You can argue from first principles and then ship the pragmatic thing.. Qualifications • 5+ years of professional software engineering experience with demonstrated technical leadership on complex systems or products. • A hands-on engineer who still enjoys coding while taking on leadership responsibilities. • Background as a Tech Lead, Senior/Staff Engineer, early engineer at a high-growth startup, or founder/co-founder of a startup. • Experience building modern web applications with frameworks such as React or Next.js, with strong product intuition and UX/design sensibility. • Backend expertise with modern frameworks such as Django, FastAPI, or Node.js, along with strong SQL and system design fundamentals. • Experience building or integrating AI/LLM-powered systems or workflows • Familiarity with modern infrastructure and tooling such as AWS, GCP, or Azure, along with workflow or systems tooling (e.g., Temporal, Airflow, Prefect, Redis, OAuth). • Bonus experience with distributed systems, ETL/data pipelines, DevOps tooling (Kubernetes, Helm), or mobile development. • Strong communicator who is comfortable collaborating with cross-functional teams and occasionally engaging with customers. • Motivated, intellectually curious, and driven to build exceptional products with a high-performing team. • Located in or willing to relocate to Boston, MA. • US Person. • Veterans strongly encouraged to apply. Benefits Belisar offers top-tier benefits for full-time employees, including: • Equity opportunity. • Platinum Healthcare: comprehensive medical, dental, and vision coverage for you and your dependents, fully covered by Belisar. • Basic Life/AD&D and long-term disability insurance fully covered, with the option to purchase additional life insurance for you and your dependents. • Relocation assistance available.