Using data from the Comparative National Elections Project 2004 and 2009 South African post-elections surveys, this paper argues that political discussion within interpersonal discussant networks plays a primary role in shaping political attitudes and vote choice in South Africa. The extent of partisan homogeneity or heterogeneity within discussant networks has important yet distinct implications for voting behaviour. While homogeneous discussion networks tend to encourage stronger partisan loyalties and fewer defections in vote choice, people in heterogeneous networks show less consistency in their attitudes and behaviour during elections. The analysis also shows how momentous socio-political events at the time of a particular election can change the nature of social networks, with important consequences for electoral outcomes.