Behaviour change is central to the prevention of many population health problems, yet it is typically difficult to initiate and sustain. This paper reports on an evaluation of a water, sanitation and hygiene (WASH) intervention in mid-western Nepal, with particular focus on the drivers and barriers for handwashing with soap/ash and elimination of open defecation. The research was conducted during October-November 2014, two and half years following the intervention's end-point. Qualitative data were collected from the target community (n = 112) via group discussions, interviews and drawings/stories of 'most significant change'. Households' handwashing/water facilities and toilets were observed. Analysis was informed by a model that highlights environmental, psychosocial and technological factors that shape hygiene behaviours across multiple levels, from the habitual to the structural (Dreibelbis et al. 2013). Findings indicate the intervention has supported development of new norms around hygiene behaviours. Key drivers of sustained hygiene behaviour were habit formation, emotional drivers (e.g. disgust, affiliation), and collective action and civic pride; key constraints included water scarcity and socio-economic disadvantage. Identifying and responding to the drivers and constraints of hygiene behaviour change in specific contexts is critical to sustained behaviour change and population health impact.