Exclusive breastfeeding (EBF) during the first 6 months of life is crucial for optimizing child growth, development and survival, as well as the mother's wellbeing. Mother's employment may hinder optimal breastfeeding, especially in the first 6 months. We assessed the effectiveness of a baby-friendly workplace support intervention on EBF in Kenya. This pre-post intervention study was conducted between 2016 and 2018 on an agricultural farm in Kericho County. The intervention targeted pregnant/breastfeeding women residing on the farm and consisted of workplace support policies and programme interventions including providing breastfeeding flexi-time and breaks for breastfeeding mothers; day-care centres (crèches) for babies near the workplace and lactation centres with facilities for breast milk expression and storage at the crèches; creating awareness on available workplace support for breastfeeding policies; and home-based nutritional counselling for pregnant and breastfeeding women. EBF was measured through 24-h recall. The effect of the intervention on EBF was estimated using propensity score weighting. The study included 270 and 146 mother-child dyads in the nontreated (preintervention) group and treated (intervention) group, respectively. The prevalence of EBF was higher in the treated group (80.8%) than in the nontreated group (20.2%); corresponding to a fourfold increased probability of EBF [risk ratio (RR) 3.90; 95% confidence interval (CI) 2.95-5.15]. The effect of the intervention was stronger among children aged 3-5 months (RR 8.13; 95% CI 4.23-15.64) than among those aged <3 months (RR 2.79; 95% CI 2.09-3.73). The baby-friendly workplace support intervention promoted EBF especially beyond 3 months in this setting.