To what extent do social networks shape a person's vote choice? Using data on political networks gathered during a novel, multi-wave panel study conducted during the 2010 election cycle in the UK, we argue that although people may choose to discuss politics more often with those who hold similar political views, remaining disagreements in political discussion networks can still have a substantial impact on vote choice. Our study is the first large scale, general population sample survey to track changes in an individual's named political discussion partners over the course of an election campaign, and thus provides a unique opportunity to study the simultaneous processes of selection and influence in campaign-related political discussion. We use these data to identify two social processes at work during the 9 months prior to the election: "selection'', or the likelihood that people choose discussion partners based on their political views, and "influence'', the convergence of views between discussion partners. We find limited evidence that people select like-minded political discussants, but clear support for social influence on vote choice.