Objective To examine the impact of a pre‐bariatric surgery physical activity intervention (PAI), designed to increase bout‐related (≥10 min) moderate to vigorous PA (MVPA), on health‐related quality of life (HRQoL). Methods Analyses included 75 adult participants (86.7% female; BMI = 45.0 ± 6.5 kg m−2) who were randomly assigned to 6 weeks of PAI (n = 40) or standard pre‐surgical care (SC; n = 35). PAI received 6 individual weekly counseling sessions to increase walking exercise. Participants wore an objective PA monitor for 7 days and completed the SF‐36 Health Survey at baseline and post‐intervention to evaluate bout‐related MVPA and HRQoL changes, respectively. Results PAI increased bout‐related MVPA from baseline to post‐intervention (4.4 ± 5.5 to 21.0 ± 21.4 min day−1) versus no change (7.9 ± 16.6 to 7.6 ± 11.5 min day−1) for SC (P = 0.001). PAI reported greater improvements than SC on all SF‐36 physical and mental scales (P < 0.05), except role‐emotional. In PAI, better baseline scores on the physical function and general health scales predicted greater bout‐related MVPA increases (P < 0.05), and greater bout‐related MVPA increases were associated with greater post‐intervention improvements on the physical function, bodily pain, and general health scales (P < 0.05). Conclusions Increasing PA preoperatively improves physical and mental HRQoL in bariatric surgery candidates. Future studies should examine whether this effect improves surgical safety, weight loss outcomes, and postoperative HRQoL.