Background: Adult participation in sport is associated with important positive psychosocial outcomes. Despite the multitude of benefits that have been linked to sport participation, adult participation rates in Canada remain low. Parents with young children represent a demographic that may benefit considerably from sport participation, given the prevalence of inactivity coupled with increased levels of psychosocial distress among this group. This study aims to evaluate the efficacy of two types of sport participation (individual sport and team sport) on key psychosocial outcomes compared with a "personal time" control condition among parents with young children. Methods/design: The three-arm, parallel design, single-blind, randomized controlled trial will compare a team sport condition, an individual sport condition, and a "personal time" control condition over 3 months. Parents are eligible if they have a child under 13 years of age, are not participating in a sport at baseline, and are not meeting Canadian Physical Activity Guidelines. Psychosocial variables (quality of life, relationship satisfaction, social functioning, parental stress, and enjoyment) will be assessed at baseline, 6 weeks, and 3 months. A total of 161 parents have been recruited thus far from the Greater Victoria region in British Columbia, Canada. The study is ongoing with a target goal of 240 participants and an anticipated completion date of December 2021. Discussion: This protocol describes the implementation of a randomized controlled trial that evaluates the effectiveness of sport participation for increasing positive psychosocial outcomes. This information could prove useful for future adult sport participation and potentially inform public health initiatives involving parents and families. Trial registration: ClinicalTrials.gov, NCT02898285. Registered 13 September 2016.