Acceptance and commitment therapy (ACT) is an adapted form of cognitive behavioural therapy. ACT focuses on how thinking affects behaviour and promotes psychological flexibility. The prevalence of psychological distress among people living with cardiovascular disease (CVD) and/or type 2 diabetes mellitus (T2DM) is high, and ACT may offer an alternative treatment approach. This scoping review explored the use of ACT as an intervention to support adults living with CVD and/or T2DM. A systematic search of the literature resulted in the inclusion of 15 studies. Studies were reviewed using the Joanna Briggs Institute approach to conducting scoping reviews. Most studies (n = 13) related to people living with T2DM, and most (n = 10) used a pre-post design, four studies were randomised controlled trials, and one was a qualitative study. Eight studies reported an improvement in the outcome(s) assessed post-intervention, suggesting that ACT was an acceptable and valid intervention to support people living with CVD or T2DM. However, studies were underpowered and only limited studies involved people living with CVD. ACT was assessed as a valuable approach to improve a range of patient-reported outcomes for those living with CVD or T2DM, and further research involving robust study designs and larger cohorts are warranted.