Mental health task shifting is a potential way to address the burgeoning treatment gap for mental illness. Easily available and accessible digital technology can be utilised to continuously engage grassroot level health workers (for example, Accredited Social Health Activists (ASHAs). However, the impact of such a strategy is not yet systematically evaluated. In this randomised controlled trial, longitudinal hybrid training of ASHAs [1 day in-person classroom training and seven online sessions (ECHO model), aimed to screen and refer to commonly prevalent mental health issues in communities] was compared with traditional one-day in-person classroom training. ASHAs (n = 75) from six Primary Health Centres in Ramanagara district, Karnataka, India were randomized into study (SG-ASHAs) and control (CG-ASHAs) groups. After excluding drop-outs, 26 ASHAs in each group were included in the final analysis of the scores on their Knowledge, attitude, and practices (KAP) in mental health. Two house-to-house surveys were conducted by both groups to identify and refer possible cases. The number of screen positives (potential persons with mental illnesses) and the KAP scores formed the outcome measures. Online sessions for SG-ASHAs were completed over 18 months, the COVID-19 pandemic being the main disruptor. SG-ASHAs identified significantly higher number of persons with potential alcohol use disorders [n = 873 (83%); p ≤ 0.001] and common mental disorders [n = 96(4%); p = 0.018], while CG-ASHAs identified significantly higher number of those with potential severe mental disorders [n = 61(61.61%); p ≤ 0.001]. As regards KAP, after controlling for baseline scores, the time effect in RMANOVA favoured SG-ASHAs. Mean total KAP score increased from 16.76 to18.57 (p < 0·01) in SG-ASHAs and from 18.65 to 18.84 (p = 0.76) in CG-ASHAs. However, the Time-group interaction effect did not favour either (F = 0.105; p = 0.748). Compared to traditional training, mentoring ASHAs for extended periods is more impactful. Easily accessible digital technology makes the latter feasible. Scaling up such initiatives carry the potential to considerably improve treatment access for those in need.