Abstract: Understanding election campaigns is no longer limited to focusing only on traditional electoral players such as political parties. In recent years online campaigning organisations have featured in election campaigns as actors trying to persuade voters to mobilise around, mostly, progressive policy concerns. For example, MoveOn in the United States has been a notable actor generating citizen activism and support for the Democratic Party. In an era where citizen engagement in traditional political institutions is in decline, the emergence of these new forms of online participatory politics is distinctive. In Australia, organisations like GetUp! have become part of mainstream political debate, while also bringing a 'rapid response' social movement sensibility to citizen mobilisation during election campaigns. Using case study analysis, this article shows that GetUp! became one of the most prominent civil society organisations active during the Australian 2010 federal election campaign. Our argument is substantiated through focusing on GetUp!'s strategic repertoire and tactics, including its distinctive online approach to organising, communications, and mobilising members. Analysis of election-specific traditional media coverage of the organisation also reveals the political mainstreaming of its campaigning work.