Abstract Background Dementia caregiving is a dynamic and multidimensional process. To gain a comprehensive understanding of informal caregiving for people living with dementia (PLWD), it is pivotal to assess the quality of life (QoL) of informal caregivers. Objective To evaluate whether the care–recipient relationship type predicts changes in the QoL of informal caregivers of PLWD over a two-year period. Methods This was a secondary analysis of longitudinal data. The data were drawn from two waves of linked data from the National Health and Aging Trends Study (NHATS) and the National Study of Caregiving (NSOC) (2015: NHATS R5 & NSOC II; 2017: NHATS R7 & NSOC III). Caregivers were categorized into spousal, adult–child, “other” caregiver and “multiple” caregivers. QoL was assessed through negative emotional burden (NEB), positive emotional benefits and social strain (SS). Generalized estimating equation modelling was used to examine changes in caregivers’ QoL outcomes across types of relationship over time. Results About, 882 caregivers were included who linked to 601 PLWD. After adjusting caregivers’ socio-demographics, “other” caregivers had lower risk of NEB and SS than spousal caregivers (OR = 0.34, P = 0.003, 95%CI [0.17, 0.70]; OR = 0.37, P = 0.019, 95%CI 0.16, 0.85], respectively), and PLWD’s dementia status would not change these significance (OR = 0.33, P = 0.003, 95%CI [0.16, 0.68]; OR = 0.31, P = 0.005, 95%CI [0.14, 0.71], respectively). Conclusions The study demonstrates that spousal caregivers face a higher risk of NEB and SS over time, underscoring the pressing need to offer accessible and effective support for informal caregivers of PLWD, especially those caring for their spouses.