To evaluate the impact of a peer facilitator (PF) approach for improving mothers' knowledge and practices relating to maternal and child nutrition. A quasi-experimental design nested within a large-scale integrated nutrition programme, Suaahara, in Nepal. Suaahara interventions were implemented in all study sites, but peer facilitators were used in only half of the study sites. Rural, disadvantaged villages in three districts of Nepal: Bhojpur, Bajhang and Rupandehi. Mothers of children aged 6-23·9 months (n 1890). Differences over time between comparison (C) and intervention (I) groups show that the PF approach had a significant positive impact on several indicators of mothers' knowledge and practices relating to maternal and child nutrition: (i) knowing that fruits and vegetables are good for children 6-23·9 months (C: -0·7, I: 10·6; P=0·03); (ii) child dietary diversity (C: 0·02, I: 0·04; P=0·02); (iii) child minimum dietary diversity (≥4 of 7 food groups; (C: 6·9, I: 16·0; P=0·02); (iv) maternal dietary diversity (C: 0·1, I: 0·4; P=0·01); and (v) maternal minimum dietary diversity (≥4 food groups; C: 3·6, I: 14·0; P=0·03). Additionally, exposure to a PF three or more times in the past 6 months was positively associated with a small improvement in maternal (β=0·06, P=0·04) and child (β=0·06, P=0·02) dietary diversity scores. Improvements were not observed in maternal health-seeking behaviours such as number of antenatal care visits. Peer mobilization is a potential approach for improving health- and nutrition-related knowledge and behaviours among women in hard-to-reach communities of Nepal.