Background Fibromyalgia syndrome (FMS) is both a challenging and disabling condition. The International Association for the Study of Pain (IASP) classifies FMS as chronic primary pain, and it can negatively impact individuals’ functioning including social, psychological, physical and work-related factors. Notably, while guidelines recommend a biopsychosocial approach for managing chronic pain conditions, FMS assessment remains clinical. The WHODAS 2.0 is a unified scale to measure disability in the light of the International Classification of Functioning, Disability and Health. Thus, this study aimed to evaluate the reliability and validity of the Brazilian version of WHODAS 2.0 for use in individuals with FMS. Methods Methodological study of the validity and reliability of the Brazilian version of the 36-item WHODAS 2.0 with 110 individuals with FMS. The instrument gives a score from 0 to 100, the higher the value, the worse the level of functioning. We assessed participants with Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) (0–100), Fibromyalgia Impact Questionnaire (FIQ) (0–10) and Beck Depression Inventory instrument (BDI) (0–63). The construct validity, internal consistency, and test–retest stability. We used SF-36, FIQ and BDI to study construct validity analysis. For statistical analysis, we performed the intraclass correlation (ICC), Spearman correlation, and Cronbach's alpha, with a statistical level of 5%. Results Most participants were female (92.27%), aged 45 (± 15) years. The test–retest reliability analysis (n = 50) showed stability of the instrument (ICC = 0.54; ρ = 0.84, p < 0.05). The test–retest correlation between the domains was moderate to strong (ρ > 0.58 and < 0.90). Internal consistency was satisfactory for total WHODAS 2.0 (0.91) and also for domains, ranging from 0.44 to 0.81. The construct validity showed satisfactory values with all moderately correlated with WHODAS 2.0 instruments (> 0.46 and < 0.64; p < 0.05). WHODAS 2.0 evaluates the functioning encompassing components of health-related quality of life, functional impact, and depressive symptoms in those with FMS. Conclusions WHODAS 2.0 is a reliable and valid instrument to evaluate functioning of Brazilians with FMS. It provides reliable information on individuals' health through of a multidimensional perspective, that allows for individual-centered care.