This article establishes a model of likely campaign effectiveness, before examining the intensity of constituency campaigning at the 2010 general election in Britain and its subsequent impact on electoral outcomes, using both aggregate and individual level data. It shows that constituency campaigning yielded benefits in varying degrees for all three main parties and that Labour’s constituency campaign efforts were effective despite the electoral context, and ultimately affected the overall outcome of the election. These findings have significant implications for our understanding of the circumstances under which campaigns are likely to be more or less effective, and provide further evidence that a carefully managed campaign stands the most chance of delivering tangible electoral payoffs.