Cash transfer programmes form an integral part of nutrition, health, and social protection policies worldwide, but the mechanisms through which they achieve their health and nutritional impacts are incompletely understood. We present results from a process evaluation of a combined participatory women's groups and cash transfer programme to improve low birth weight in rural Nepal. We explored the ways in which context, implementation, and mechanism of the intervention affected beneficiary women's agency over cash transfers. Informed by a grounded theory framework, we conducted and analysed semi-structured interviews with 22 beneficiary women, 15 of their mothers-in-law, 3 of their elder sisters-in-law and 20 husbands, as well as a focus group discussion with 7 supervisors of the women's group intervention. Our study reveals how women's group facilitators, their supervisors and community members developed a shared dynamic around persuading and compelling recipients of unconditional cash transfers into spending them according to criteria developed by the group. We found these dynamics effectively constituted ‘soft conditions’ on beneficiary spending which restricted women's ability to make decisions over their cash transfers, but also increased their likelihood of spending them on their own pregnancy. Our findings demonstrate the importance of understanding how programmes are implemented and responded to in order to understand their implications for beneficiary agency and empowerment.