This research aimed to examine the factors affecting the participation of female rural–urban migrants in online marketplaces, and the welfare gains and their distribution. Our analysis was based on a unique dataset of rural households, villages, and rural–urban migrants in Thailand and Vietnam. Online market participation is classified into three activities: financial transactions, trading, and business. We accounted for the endogeneity issue of online market participation in the assessment of welfare impact by using an instrumental variable approach. Our results show that participation has a positive effect on the consumption of female migrants only when they participate in the complete bundle of online market activities. In addition, we find that the poor benefit insignificantly from online marketplaces. This raises a concern about increasing welfare inequality and suggests the poor should be supported so they are not left behind.