BACKGROUND: Yoga is a safe, effective, and popular practice among older adults, and amenable to online delivery. The Gentle Years Yoga randomised controlled trial compared the impact of a chair-based yoga programme to usual care on the health-related quality of life of older adults with multimorbidity. This embedded, longitudinal process evaluation qualitatively explored experiences and acceptability of online delivery of the trial intervention. METHODS: A subset of trial participants randomised to receive the 12-week online yoga programme, together with the trial yoga teachers, were purposively recruited to semi-structured interviews. Individual interviews were conducted via Zoom or telephone, audio-recorded, independently transcribed, and thematically analysed. Online observations were conducted of one class delivered by each teacher. RESULTS: Eighteen yoga participants (66-91 years; 2-8 chronic health conditions) and nine teachers were interviewed once (N = 12) or twice (N = 15) from October 2020 to April 2022. Five themes predominated, common to both groups. (1) Accessibility. Reduced communication and engagement inherent to online delivery were mostly outweighed by its removal of access barriers and provision of anonymity and distraction-free environment. (2) Technology issues. While digital literacy was variable and a barrier for some, simplified access procedures and basic audiovisual instruction optimised class engagement. (3) Delivery adaptations. Key facilitation techniques included simple, repetitive instructions, increased demonstration, personalised communication, and visibility-enhancing clothing. (4) Safety. Concerns were minimal, and mostly related to restricted visual and positional information inherent to face-to-face classes. (5) Implications and implementations. Online delivery was considered viable and potentially appealing for anyone experiencing issues accessing face-to-face classes outside the home. Potential solutions to online attendance barriers included equipment loan schemes and digital learning courses using existing community-based infrastructures. CONCLUSIONS: Online chair-based yoga classes were feasible and acceptable to participants and teachers, and preferrable to face-to-face delivery by some. IT issues were minimal, and mainly resolvable through simple access processes and educational information. Accessibility advantages suggest online yoga may be suitable for a broad demographic, independent of age or health status. Establishing connections with existing health and community-based organisations presents a potential pathway for developing an equipment loan scheme to improve accessibility for those with financial access barriers. TRIAL REGISTRATION: ISRCTN ISRCTN13567538. Registered 18 March 2019.