12 candidates made the ballot to replace Menino, with state representative Marty Walsh and at-large city councilor John R. Connolly advancing to the general election.

[39] Connolly's campaign was considered to have little chance of succeeding if Menino decided to run for re-election, as the incumbent was highly popular in the city.

[39] On March 28, Menino announced that he would not be seeking re-election, stating that health issues were preventing him from carrying out his tasks as mayor to a satisfactory standard.

[44] Several other candidates, including City Councillors Michael P. Ross and Charles Yancey, former state representative Charlotte Golar Richie, and Boston School Committee member John Barros announced campaigns over the following weeks.

[46] Upon his entry into the race Walsh had demonstrated organizational strength by gathering the required signatures to get on the ballot in a single day, which impressed political insiders and showcased the influence of the labor unions who were supporting his candidacy.

[47] By mid-September, it was suggested by radio station WBUR-FM that a clear top tier of candidates had arisen in the race, consisting of Connolly, Walsh, Golar Richie, Arroyo and Conley.

[71] However, Walsh's campaign was boosted by large spending by labor unions, who were dissatisfied with Connolly due to his staunch support for charter schools.

[72] Connolly's base of support largely came from his home neighborhood of West Roxbury and the relatively affluent communities in Boston's west, while Walsh had support from both the more working-class, culturally conservative areas in South Boston and from left-wing activists who had been invigorated by Elizabeth Warren's successful campaign for U.S. Senate the previous year.