PurposeWe examined the impact of a leadership support training intervention implemented prior to the coronavirus (COVID-19) pandemic on support behaviors specific to COVID-19 during the pandemic. Primary intervention targets (i.e. family-supportive supervisor behaviors and sleep leadership behaviors) were explored as mediators between the intervention and supportive COVID-19 leadership behaviors.Design/methodology/approachA cluster randomized controlled trial intervention was implemented with service members and their supervisors in the Army and Air National Guard throughout 2017–2019. Follow-up survey data were collected after the intervention, including during the COVID-19 pandemic in 2020. Direct and indirect intervention effects were tested.FindingsA pre-COVID intervention targeting leader support for family and sleep health had a direct effect on leader support specific to the COVID-19 pandemic. Additionally, sleep leadership, but not family-supportive supervisor behaviors, mediated the intervention effects on supportive COVID-19 leadership. These findings suggest that certain leadership training interventions can transfer across knowledge domains and time.Practical implicationsFindings from this study demonstrate that training leaders on support behaviors improves their ability to support employees during the COVID-19 pandemic and may translate to crisis leadership in other contexts.Originality/valueWe examined the long-term effects of an intervention that was implemented approximately 1–2 years prior to the COVID-19 pandemic on leadership support behaviors specific to the pandemic. Our findings contribute to the leadership, training, and organizational intervention literatures, and have implications for how leaders can support employees during crises.