Objective: Evidence suggests that treatment side‐effects of prostate cancer (CaP) substantially affect the psychosocial well‐being of affected men and their partners. However, this phenomenon is poorly understood among high risk (1 in 4) Black African (BA)/Black Caribbean (BC) men and their partners, as they are currently under‐represented in global research on CaP survivorship. This study explored the psychosocial experiences of BA/BC men with CaP and their partners in the United Kingdom as they lived through the side effects of CaP treatment within their own sociocultural and marital contexts. Methods: Using constructivist grounded theory methodology, interviews and focus groups were conducted with eligible men (n = 25), partners (n = 11), and health care professionals (HCPs) (n = 11) recruited in England. Data were iteratively analysed using constant comparison following the key stages of initial, focused, and theoretical coding until saturation was achieved. Results: Data analysis culminated in the development of a substantive theory “man in the driving seat,” which describes the experiences of BA/BC men with CaP and their partners within their context. Culturally informed gender roles and identities influenced how men and partners responded and coped with the side effects of CaP treatment. There was a hierarchy of power within the BA/BC relationship, in which men were dominantly positioned as leaders, whilst partners mostly operated from a supportive but “accepting” position. Conclusion: Inclusive and culturally sensitive individual and couple‐focused psychosocial support, which is devoid of stereotyping and recognises the experiences of both BA/BC men and their partners is recommended.