While symptoms of insomnia are common in older adults with mild cognitive impairment (MCI) and predict future cognitive decline, a robust evidence base for treating insomnia in MCI is lacking. This study investigated the feasibility of recruiting and delivering a digital cognitive behavioural therapy for insomnia (dCBT-I) in this group. In a parallel open-label randomised-controlled feasibility trial, participants were recruited and screened via the internet and assessed for MCI using videoconference methods. Eligible participants were randomised to dCBT-I (Sleepio, 6 weekly sessions) or control (3 online modules of sleep health education) over a 12-week period. Inclusion criteria included adults aged ≥ 50 years, Insomnia Severity Index (ISI) > 10, and clinical criteria of MCI on a neuropsychological battery. The primary outcomes were the proportion of participants who met screening and randomisation criteria, and their recruitment pathway (clinic vs. online). A secondary outcome was the effect size of the difference in ISI between groups at week 12. Recruitment occurred March-August 2023 (dCBT-I = 19; control = 21; 30 females; mean [SD] age = 59.7 years [7.3]; ISI = 17.0 [3.7]). 37% of participants issued a pre-screening number (n = 246) were eligible to attend online screening. 47% of those issued a screening number (n = 90) were eligible to be randomised (n = 42), with 2 not proceeding (final n = 40). dCBT-I improved 12 weeks ISI compared to control (Cohen's d [95% CI] -1.6 [-2.4 to -0.8]). 79% of participants completed ≥ 4 sessions. This population can be recruited through online pathways and follow the protocol as well as adhere to the intervention of this remotely conducted trial. Trials Registration: ClinicalTrials.gov Registry: (NCT05568381 registered 03/10/2022).