Background: Studies have shown that children and adolescents with autism and their relatives present a high level of stress and more family problems, impacting parents’ and caregivers’ quality of life (QoL). Despite studies on this subject, there is no specific questionnaire to evaluate QoL in parents or caregivers of children and adolescents with an autistic spectrum disorder (ASD) in Brazil. Therefore, this study’s primary purpose was to develop and validate a specific questionnaire to evaluate QoL in these individuals. Methods: The study was performed using the following steps: development of the ASD Parent/caregiver QoL questionnaire (autistic spectrum disorder parent/caregiver quality of life—ASDPC-QoL), subjective evaluation, validation of the questionnaire by the Delphi method, assessment of internal consistency, responsiveness, and reliability of the ASLPC-QoL, and administration of the questionnaire to 881 Brazilian ASD caregivers or parents. ASDPC-QoL comprises 28 questions divided into four domains (social, concerns, physical and mental health) with good psychometric properties (reproducibility, reliability, internal consistency, responsiveness, and validity). Results: Our data showed that worries and physical health were the domains with the lowest scores in ASDPCA-QoL. ASDPCA-QoL did not differ among gender and age of child considering the total and all domains. Older participants (≥41 y/o) presented the best scores for social and worries domains but did not differ in other domains and the total. Parents or caregivers of ASD children diagnosed for more than three years have better mental and physical health domains than those recently diagnosed (up to 1 year) but did not differ in the total and other domains. Individuals with a partner and with the highest educational level present the best score for the social domain. Employed individuals showed better scores than unemployed ones for all domains and the total, except for worries, which did not differ. It also occurred comparing the individuals that do not use antidepressants and the ones that use them. Conclusions: Assessing and better understanding the QoL of caregivers is highly relevant. By understanding the social, worries, physical, and emotional health domains of caregivers, it is possible to track harmful aspects, prevent and treat pathologies, in addition to assisting in the implementation of effective public policies.