In light of the individualisation, dispersal and pervasive monitoring that characterise work in the ‘gig economy’, the development of solidarity among gig workers could be expected to be unlikely. However, numerous recent episodes of gig workers’ mobilisation require reconsideration of these assumptions. This article contributes to the debate about potentials and obstacles for solidarity in the changing world of work by showing the processes through which workplace solidarity among gig workers developed in two cases of mobilisation of food delivery platform couriers in the UK and Italy. Through the framework of labour process theory, the article identifies the sources of antagonism in the app-mediated model of work organisation and the factors that facilitated and hindered the consolidation of active solidarity and the emergence of collective action among gig workers. The article emphasises the centrality of workers’ agential practices in overcoming constraints to solidarity and collective action, and the diversity of forms through which solidarity can be expressed in hostile work contexts.