In support of measures to prevent, detect, and respond to nuclear security events, nuclear forensic science provides the technical information necessary to assess the origin and history of nuclear and other radioactive materials out of regulatory control in the context of international legal instruments and national laws related to nuclear security. In order to help partner countries meet their nuclear security objectives, the Los Alamos National Laboratory and the Lawrence Livermore National Laboratory, through partnership with the U.S. Department of Energy’s National Nuclear Security Administration (DOE/NNSA) Office of Nuclear Smuggling Detection and Deterrence (NSDD), have assisted over 20 countries to develop, sustain, and advance indigenous nuclear forensic capabilities through in-person scenario-based policy discussions, hands-on laboratory-based trainings, material sample exchanges, and laboratory peer interaction. The ongoing COVID-19 pandemic has adversely impacted the ability of nuclear forensic assistance providers to implement hands-on capacity building and to carry out in-person interaction. As nuclear forensic examinations support law enforcement investigations and nuclear security vulnerability assessments, unique strategies for virtually developing, testing, and sustaining nuclear forensic capabilities are essential to enable sustained assurances that partner countries are able to respond to nuclear security events. In order to meet the challenge, the Los Alamos National Laboratory and the Lawrence Livermore National Laboratory developed and implemented unique virtual interaction engagement models for continued engagement with international partners, with an emphasis on practical applications of nuclear forensics in support of investigations. To ensure a sufficient nuclear forensics workforce, the Los Alamos National Laboratory and the Lawrence Livermore National Laboratory continue to deliver high-quality capacity building in a time where traditional, in-person capacity building curriculum delivery is not available and continue to develop the next generation of nuclear forensic practitioners by creating virtual pathways for dedicated and cross-disciplinary capacity building opportunities.