Many qualitative studies report the post-diagnostic care experiences of carers and people living with dementia; however, this is not often accompanied by opportunities to hear the corresponding views of their health care professionals and how this triadic relationship functions. The aim of this review was to identify and thematically synthesize the experiences of health care services reported by people living with dementia, their carers and health care professionals. Medline, PsycINFO, Embase and CINAHL were searched from inception to 31 July 2019 for qualitative research including people living with dementia, carers and health care professionals. Data were coded and thematically synthesised using NVivo. Of 10,045 search results, 29 papers relating to 27 studies were included in the final synthesis, including 261 people living with dementia, 444 carers and 530 health care professionals. Six themes emerged related to the functioning of a dementia care triad: (1) involving the person living with dementia, (2) establishing expectations of care and the roles of the members of the triad, (3) building trust, (4) effective communication, (5) continuity of care and (6) understanding the unique relationship dynamics within each triad. The interactions and complexity of triadic dementia care relationships further our understanding of how to improve dementia care. Awareness of possible diverging attitudes highlights areas of necessary improvement and further research into facilitating engagement, such as when multiple professionals are involved or where there are mismatched expectations of the roles of triad members. In order to operate efficiently as a triad member, professionals should be aware of how pre-existing relations can influence the composition of a triad, encourage the involvement of the person living with dementia, clarify the expectations of all parties, establish trusting relationships and enable communication within the direct triad and beyond.