The objective of the review was to explore the relevance of the relationship of compassion and attachment to mental health. APAPsycInfo, APAPsycArticles, CINAHL, MEDLINE, Social Science Database, Sociology Database, PTSDpubs, Pubmed, and Web of Science were searched from their inception until November 9, 2021. Peer-reviewed empirical studies exploring the compassion–attachment relationship in individuals with mental health difficulties through outcome measures were included. Studies were excluded if non-empirical, with non-clinical/subclinical samples, in a language other than English and if they did not consider the compassion–attachment relationship. Risk of bias was assessed through The Newcastle–Ottawa Scale and the Downs and Black Checklist. Seven eligible studies comprising 4839 participants were identified, with low to moderate risk of overall bias. Findings indicated a more straightforward relationship between self-compassion and secure attachment and confirmed the relevance of compassion and attachment to psychological functioning. Limitations concerned study design, the use of self-report measures, and low generalisability. While suggesting mechanisms underpinning compassion and attachment, the review corroborates the role of secure attachment and self-compassion as therapeutic targets against mental health difficulties. This study is registered on PROSPERO number CRD42021296279.