Prior scholarship has paid little attention to the political outcomes deriving from the use of private social media like WhatsApp. A few studies address the impact of the broad concept of “WhatsApp political talk” on various forms of political participation and knowledge. However, and despite the opportunities for strong-tie connection and privacy provided by these platforms, which might pave the way for unfiltered discourse and the radicalisation of viewpoints, we still lack robust evidence on the effects of their political usage on polarisation. This paper fills that gap by focusing on WhatsApp and both the ideological and affective dimensions of polarisation. In doing so, we do not only assess the relationship between “WhatsApp political conversation” and individuals’ ideological/affective polarisation, but also consider (1) different types of political conversations and (2) different political experiences within the platform (e.g.: receiving news, sharing news), arguing that distinct conversations and experiences may lead to distinct outcomes. Likewise, building on recent literature emphasising the close link between affective and false ideological polarisation, we also examine the impact of WhatsApp political usage on ideological misperceptions and evaluate the latter’s mediating role in the WhatsApp-affective polarisation relationship. To this end, we concentrate on the paradigmatic case of Spain, where 90% of the population uses this platform, and rely on the first representative survey (n = 800) that collects detailed data on individuals’ WhatsApp practices and their political attitudes simultaneously. To complement our statistical findings, we harness the information deriving from a comprehensive set of ten focus groups that involve more than 50 participants.