Democrat Colleen Hanabusa, who was first elected to represent the 1st district in 2010, successfully ran for re-election. Roy Wyttenbach II unsuccessfully challenged Hanabusa in the Democratic primary.
Former U.S. Representative Charles Djou, who represented the 1st district from May 2010 until January 2011, sought and received the Republican nomination to challenge Hanabusa again. He defeated C. Kaui Amsterdam and John Giuffre in the Republican primary.
Gabbard received endorsements from the Sierra Club, Women Under Forty PAC,Emily's List, and MauiTime. Hannemann and Gabbard also differed on the issue of same-sex marriage. Gabbard was opposed to the Defense of Marriage Act and to a proposed Hawaii state constitutional amendment that would define marriage as between a woman and a man, while Hannemann supported DOMA. Gabbard had previously opposed same-sex marriage, but during the primary campaign, promised to work to repeal DOMA and co-sponsor the Respect for Marriage act. Voters initially doubted the sincerity of her new views on the issue.
Gabbard filed a 270-page complaint against Hannemann's spending, saying that his campaign broke campaign finance laws by failing to report 2012 travel and polling expenses and improperly dealt with Hanneman's salary from a tourism association.
Candidates Marx, Gabbard, and Kia'aina debated on June 5, and Marx, Gabbard, Kia'aina and Hannemann debated in early July.
Gabbard's ratings in the polls increased steadily and Hannemann's dropped throughout the primary campaign,; as of August 6, she was leading against Hanneman 49% to 29%. On August 11, she defeated Hanneman by twenty points, winning the primary. The Honolulu Star-Advertiser described her win as the "improbable rise from a distant underdog to victory". Gabbard credited grassroots support as the reason for her come-from-behind win in the primary. She decided to resign her seat on the City Council, stating that she wanted to prevent the cost of a separate special election, and resigned on August 16.
Rafael "Del" del Castillo, attorney and patients' rights advocate