High levels of parental stress can adversely affect both parents and children, leading to negative psychological outcomes. The present study consists of two randomised controlled trials investigating the effectiveness of a 14-day mindfulness- and compassion-based parenting programme delivered through instant text messaging in reducing parenting stress. Studies 1 and 2 recruited 222 and 271 parents in August 2021 and January 2022, respectively. All participants had at least one child studying in nursery or primary school. Participants were randomly assigned to either an intervention group or a waitlist control group. Assessments were conducted before the intervention, immediately following the intervention and 14 days after the intervention. During the 14-day intervention, 14 audio recordings (ranging in length from 12 to 17 min) introducing parenting skills as well as mindfulness and compassion exercises were sent to the participants through WhatsApp and Signal. The primary outcome of both studies was parenting stress. Mental well-being, interpersonal mindfulness in parenting and parenting behaviours were measured as secondary outcomes. Data were analysed using linear mixed models with full maximum likelihood estimation. A significant time by group interaction effect on parenting stress was found in both studies. In both studies, intervention effects on parenting stress were not sustained at 14-day follow-up. The results of the present study provided evidence that a brief, instant messaging-based parenting programme has the potential to reduce parenting stress.