A grounded theory study was employed to identify the conditions contributing to the core phenomenon of Asian American activists (N = 25) mobilizing toward thick solidarity with the Black Lives Matter (BLM) movement in 2020. The findings indicate achieving a collective oppressed identity was necessary to mobilize in thick solidarity with the BLM movement and occurred because of causal conditions: (a) experiences of COVID-19–related anti-Asian discrimination, and (b) George Floyd’s murder. Non-action, performative or unhelpful action, and action toward thick solidarity were influenced by contextual factors: (a) alignment with personal and community values, (b) awareness and knowledge, and (c) perspectives of oppression. Mobilization was also influenced by intervening factors, which included affective responses, intergenerational conflict, conditioning of “privileges” afforded by White supremacy, and the presence of organized communities. Mental health professionals and social justice advocates can apply these findings to promote engagement in the community organizing efforts of Asian American and Pacific Islander communities with the BLM movement, denounce anti-Blackness, and uphold a culpability toward supporting the Black community.