Although medical events in lung cancer screening (LCS) such as receiving scan results or interactions with clinicians are recognised as teachable moments (TMs), the views of patients about why this is the case for smoking behaviour change remain uncertain. This systematic review and metasynthesis study is aimed at identifying the reasons why patients believed that medical events during LCS act as TMs for smoking behaviour change. A search strategy was developed for use with MEDLINE, PsycINFO, EMBASE, CINAHL-P, Web of Science databases, and Google Scholar. This helped identify qualitative and mixed-method research which mentioned patients' views of how these TMs result in smoking behaviour change. After screening, final articles were critically appraised; general characteristics and data relevant to the aims were extracted to conduct a line-of-argument metasynthesis. After screening 695 papers, 11 were included. Undergoing LCS scans was seen to act on their intrinsic motivation to reduce smoking as it served as a “wake-up call” and increased awareness of the health consequences of smoking. Receiving positive or negative LCS results resulted in cessation as it was a “health scare” and challenged smoking habits. Interactions with clinicians addressed misconceptions and signposted them to specialist cessation services. Attendees believed that the following encouraged them to change their smoking behaviour: having an intrinsic motivation to quit, their beliefs on smoking and health reframed, their negative emotions appraised, and using LCS to access specialist support. In line with the TM heuristic, these experiences provided the necessary skills, confidence, and motivation to quit. Future research should explore whether the views of the clinicians match those of the attendees to address misconceptions and further develop clinical guidelines.