Although the role of lifestyle in health-related quality of life (HRQoL) outcomes has been increasingly recognized for various types of cancer, evidence in patients with non-muscle invasive bladder cancer (NMIBC) is very limited. We aimed to evaluate the longitudinal association between adherence to the 2018 World Cancer Research Fund/American Institute for Cancer Research (WCRF/AICR) lifestyle recommendations and HRQoL in patients with NMIBC. This study included 1029 patients with NMIBC recruited between May 2014 and April 2017 from the Dutch multi-centre prospective cohort study UroLife. Lifestyle and HRQoL data were collected at 6 weeks (baseline), 3 months and 15 months after diagnosis. Information on body mass index (BMI), physical activity, diet and alcohol was used to compute the standardized WCRF/AICR adherence score (0-7). HRQoL outcomes were evaluated by the EORTC QLQ-C30. Linear mixed models were used to assess longitudinal confounder-adjusted associations between the WCRF/AICR adherence score and HRQoL outcomes. Adherence to each additional WCRF/AICR recommendation was associated with better global quality of life, physical, role and social functioning, and less fatigue. We found stronger inter-individual than intra-individual associations, suggesting that associations were mainly driven by between-subject differences. Higher adherence to the BMI, physical activity and dietary recommendations was associated with better scores for most HRQoL outcomes, while adherence to the alcohol recommendation (ie, non-consumption) was associated with worse HRQoL. Following the WCRF/AICR lifestyle recommendations may improve HRQoL in patients with NMIBC. Intervention studies are needed to establish whether the association between lifestyle and HRQoL is causal.