Objective: Multiple Sclerosis (MS) is a chronic demyelinating disease of the central nervous system, resulting in a range of potential motor and cognitive impairments. The latter can affect both executive functions that orchestrate general goal-directed behaviour, and social cognitive processes that support our ability to interact with others and maintain healthy interpersonal relationships. Despite a long history of research into the cognitive symptoms of MS, it remains uncertain if social cognitive disruptions occur independently of, or reflect underlying disturbances to, more foundational executive functions. The present preregistered study investigated this directly. Method: Employing an experimental design, we administered a battery of computerised tasks online to a large sample comprising 134 individuals with MS and 134 age- and sex-matched healthy controls (HCs). Three tasks measured elements of executive function (working memory, response inhibition, and switching) and two assessed components of social cognition disrupted most commonly in MS (emotion perception and theory of mind). Results: Individuals with MS exhibited poorer working memory (d = .31), response inhibition (d = -.26), emotion perception (d = .32) and theory of mind (d = .35) compared with matched HCs. Furthermore, exploratory mediation analyses revealed that working memory performance accounted for approximately 20% of the group differences in both measures of social cognition. Conclusions: Disruptions to working memory appear to serve as one of the mechanisms underpinning disturbances to social cognition in MS. Future research should therefore examine if the benefits of cognitive rehabilitation programs that incorporate working memory training transfer to these social cognitive processes.