Background To determine long‐term quality‐of‐life (QOL) trajectories among breast cancer survivors aged 65+ (older) evaluating the effects of personality and social support. Methods Older women (N = 1280) newly examined with invasive, nonmetastatic breast cancer completed baseline assessments. Follow‐up data were collected 6 and 12 months later and then annually for up to 7 years (median 4.5 years). Quality of life was assessed using EORTC‐QLQ‐C30 emotional, physical, and cognitive scales. Optimism (Life Orientation Test), Coping (Brief COPE), and social support (Medical Outcomes Study) were assessed at baseline. Group‐based trajectory modeling identified QOL trajectories; multinomial regression evaluated effects of predictors on trajectory groups. Age, education, systemic therapy, comorbidity, and reported precancer function (SF‐12) were considered as controlling variables. Results Three trajectories were identified for each QOL domain: “maintained high,” “phase shift” (lower but parallel scores to “maintained high” group), and “accelerated decline” (lowest baseline scores and steepest decline). Accelerated decline in emotional, physical, and cognitive function was seen in 6.9%, 31.8%, and 7.6% of older survivors, respectively. Maladaptive coping and lower social support increased adjusted odds of being in the accelerated decline group for all QOL domains; lower optimism was only related to decline in emotional function. Chemotherapy was related to physical and cognitive but not emotional function trajectories. Conclusions Personality and social resources affect the course of long‐term emotional well‐being of older breast cancer survivors; treatment is more important for physical and cognitive than emotional function. Early identification of those vulnerable to deterioration could facilitate clinical and psychological support.