Objective: Asthma outcomes remain suboptimal, despite effective pharmacotherapy. Psychological dysfunction (such as anxiety) is common, and associated with poorer outcomes. We evaluated a digital mindfulness programme as an intervention to improve asthma-related quality of life for primary care patients, in a prospectively registered randomized-controlled feasibility study. Methods: We offered 'Headspace', a widely-used digital mindfulness intervention, to adults with asthma through 16 UK GP practices. Participants were randomised on a 2:1 basis to the mindfulness intervention, or waitlist control. Participants completed questionnaires (including asthma symptom control, asthma-related quality of life, anxiety, depression) at baseline, 6-week and 3-month follow-up. Results: 114 participants completed primary outcomes at 3-month follow-up (intervention 73 (71.6%), control 41 (70.7%)). Compared to baseline, the intervention group but not the control group reported significantly improved asthma-related quality of life, with a non-significant between-group difference favouring the intervention group (Mean difference = 0.16, 95%CI: -0.11 - 0.44). Intervention use varied but was generally high. Conclusions: Digital mindfulness interventions are feasible and acceptable adjunct treatments for mild and moderate asthma to target quality of life. Further research should adapt 'generic' mindfulness-based stress-reduction to maximize effectiveness for asthma, and validate our findings in a fully-powered randomized controlled trial.