Background: The burden of depression is a rapidly growing problem worldwide. Its prevalence is particularly high among individuals with chronic physical conditions such as Type 2 Diabetes (T2DM), precipitating poorer health outcomes. There is a lack of evidence around treatments that can work among such groups, particularly in Low and Middle-Income Countries (LMICs). This study aims to test the feasibility and acceptability of a culturally adapted Behavioural Activation (BA) intervention (DiaDeM) for people with T2DM and depression in two LMICs in South Asia. Methods: A multicentre, randomised-controlled feasibility trial will be conducted from March 2022 to February 2023. We will recruit 128 adults from health facilities in Bangladesh and Pakistan with a diagnosis of T2DM and depression. Using a 1:1 allocation ratio, consenting individuals will be randomised to either optimised usual care or the DiaDeM intervention. The latter will involve six face-to-face or remotely delivered BA sessions conducted by non-mental health facilitators over six to twelve weeks. Participants will be followed up at three and six months post-randomisation. Feasibility outcomes include the feasibility and acceptability of recruitment and retention, the feasibility of intervention delivery and the feasibility of data collection at baseline and follow-up (including economic data). An embedded mixed-methods process evaluation will also be carried out to inform the main trial. Conclusions: BA is a low resource intervention for depression treatment that can be optimised for delivery in LMIC settings such as South Asia. The planned feasibility trial will directly inform a larger trial to assess the effectiveness and cost-effectiveness of such an intervention in people with T2DM and depression. It will also contribute to the wider evidence base around BA in patients with chronic physical illnesses, with particular relevance to South Asian, as well as wider LMIC regions and populations. Trial registration: ISRCTN 75501608