Executive function is an area of challenge for both children with fetal alcohol spectrum disorders (FASD) and children with autism spectrum disorder (ASD). Parent ratings of everyday executive function relate to a range of outcomes, including social functioning in ASD. Comparisons between FASD and ASD have revealed both overlapping and distinct skills, but have not addressed executive function or its relation to social function. Utilizing parent report, the current study addressed relative strengths and weaknesses across scales of everyday executive function, as well as group differences between FASD and ASD. The association between executive function and social function was also evaluated. Participants with FASD (n = 23) and ASD (n = 18) were preschool and school-age children whose caregivers completed the Behavior Rating Inventory of Executive Function (BRIEF, BRIEF-2, or BRIEF-P) and the Social Responsiveness Scale, Second Edition. For both groups and all examined executive function scales, scores exceeded the normative mean, indicating challenges. The groups differed significantly on only one executive function scale: working memory. In both groups, executive function was positively correlated with social functioning, even when controlling for nonverbal IQ. The current findings highlight an overlapping association between executive function and social function in FASD and ASD.