Background: Several studies have reported low adherence to World Health Organization sedentary behavior (SB) guidelines in the early years. The purpose of this review is to examine the associations between time spent in different types of SB (screen time and habitual SB) and motor competence (MC; fundamental motor skills, fine and gross motor skills, locomotor skills, and object control and balance) in 3- to 4-year-olds. Methods: Five databases were searched on the 27th of July 2021, with an updated search conducted on the 30th of September 2023: Web of Science (core collection), PubMed Central, EMBASE (Ovid), SPORT Discus, and ERIC. Studies were included in the review if they reported on an association between time spent in SB at ages 3-4 years and MC. The methodological quality for each of the included studies was assessed using Joanna Briggs Institute critical appraisal tools. Vote counting was used to determine the direction of associations. Results: Of 5,276 total studies found in the search, 16 studies (12 cross-sectional, four longitudinal) from 11 different countries met the inclusion criteria. Seven studies examined the association between screen time and MC, six examined associations between time spent in SB and MC, and three examined the association of both screen time and time spent in SB with MC. The direction of associations was predominantly negative for both screen time and time spent in habitual SB with different components of MC. Quality of evidence ranged from three to seven out of nine for cross-sectional studies and six to nine out of 12 for longitudinal studies. Conclusions: There may be negative associations between time spent sedentary and MC in 3- to 4-year-olds. However, future studies with stronger study designs are required to confirm these associations. Findings from this review should be considered when designing strategies and interventions to promote adherence to SB guidelines.