Senior Human Resources Business Partner

About Castelion Castelion is bringing a new approach to defense development and production: one that focuses on short, iterative design cycles, rapid testing in development, and modern commercial manufacturing strategies for production at scale. We’re designing, building, and testing next-generation long-range strike weapons systems to give America and its Allies a definitive edge and deter future conflicts.

Senior HR Business Partner We are seeking a highly motivated and experienced Human Resources professional to serve as Castelion’s first HR hire. You will be a critical partner in building our company culture, supporting both hourly and salaried employees, and handling all HR functions during a period of rapid growth. As the only HR person initially, you will need to be adaptable, strategic, and hands-on, with a deep understanding of the complexities of supporting a multi-state operation.

Responsibilities Serve as a strategic HR business partner to leadership, providing guidance on workforce planning, employee relations, and company culture. Oversee the full employee lifecycle, from onboarding to offboarding, ensuring a seamless and positive experience for all employees. Lead efforts to build and strengthen Castelion’s company culture, promoting engagement and retention during a period of rapid growth.

Ensure compliance with all federal, state, and local employment laws across multiple states. Develop and implement HR policies and procedures that scale with the company’s growth. Administer benefits, compensation, and payroll for a multi-state workforce.

Act as a key resource for employees, providing guidance on HR-related matters such as performance management, professional development, and conflict resolution. Partner with leadership to ensure a safe, inclusive, and productive work environment across all sites. Contribute to strategic initiatives that support the company’s goals, such as diversity and inclusion efforts and workforce development programs.

Requirements 5 years of HR experience, with a preference for candidates with early-stage startup experience. Extensive experience managing HR functions for non-exempt employees across multiple sites, with a deep understanding of hourly workforce dynamics and challenges, including developing and implementing compliant policies under the Fair Labor Standards Act (FLSA) and other wage and hour regulations, advising managers on timekeeping, overtime, and scheduling best practices, and fostering trust and engagement to promote retention and productivity. Proven track record of supporting both hourly and salaried employees in a fast-paced environment.

Ability to handle being the sole HR person, balancing strategic and tactical responsibilities during a period of rapid growth. Demonstrated experience building and fostering company culture, particularly in high-growth environments. Strong knowledge of HR best practices, employment laws, and compliance requirements.

Ability to be hands-on and flexible with a “roll up your sleeves” approach to problem-solving. Exceptional communication and interpersonal skills, with a collaborative mindset. PHR/SPHR certification or equivalent is preferred.

Leadership Qualities: Bias to Action and Creative Problem Solving: Demonstrated ability to question assumptions and propose breakthrough ideas that lead to successful implementation.

Capable of bringing in processes, materials, or concepts from other industries to achieve efficiency gains. High Commitment, High Initiative: A genuine passion for Castelion’s mission and a strong sense of accountability.

Consistently seeks ways to contribute to technical goals and resolve blockers in the development process. Clear Communicator: Proactively communicates challenges and solutions.

Trusted to represent the company with key stakeholders such as suppliers, customers, and regulators. Capable of delivering clear, logical communications that drive clarity and eliminate ambiguity. ITAR Requirements:

To conform to U.S. Government export regulations, the applicant must be a (i) U.S. citizen or national, (ii) U.S. lawful, permanent resident (green card holder), (iii) Refugee under 8 U.S.C. § 1157, or (iv) Asylee under 8 U.S.C. § 1158, or be eligible to obtain the required authorizations from the U.S. Department of State.

Castelion is an equal-opportunity employer. Employment decisions are based on qualifications, experience, and merit, regardless of race, color, religion, gender, national origin, veteran status, disability status, sexual orientation, or any other protected class.