Physical activity (PA) is an essential component in the management of cystic fibrosis (CF). However, optimal PA programmes for patients with CF (pwcf) are yet to be defined. The aim of this PhD was to develop, implement and evaluate a PA intervention for pwcf. Formative research, consisting of an online survey with CF healthcare professionals (HCP) and semi-structured interviews with pwcf, was first conducted to inform the intervention design. HCP reported lack of patient motivation and compliance as prominent barriers to PA prescription. Pwcf expressed a preference for home-based PA to ameliorate a myriad of disease-related barriers. A theoretically-informed intervention was developed to address both HCP and pwcf barriers to PA prescription and participation, respectively. To assess the potential for successful intervention implementation, and to reduce threats to validity, it is important that feasibility trials are conducted. A randomized-controlled trial assessed the feasibility of a theoretically-informed, home-based, self-regulated and technology-enabled PA intervention and compared its effectiveness in relation to PA and quality of life (QoL) to usual care (UC). Participants (n=11) completed self-reported PA and QoL questionnaires, and accelerometry at baseline, post-12- and 18-weeks. A maximal exercise test and basic spirometry were also performed at baseline. Participants in the IG were invited to complete semi-structured exit interviews. The intervention was deemed feasible in terms of acceptability, demand, implementation and practicality. There were no statistically significant changes in PA or QoL during the intervention. The validity of the oxygen uptake efficiency slope (OUES) as a predictor for maximal oxygen consumption (VO2max) was evaluated, as VO2max has been shown to be a key indicator of longevity among pwcf. OUES at 50% of the test duration (OUES50) was identified as a reliable submaximal parameter for predicting VO2max in pwcf who are unable or unwilling to perform maximal-effort exercise due to excessive dyspnoea and/or lack of motivation.