He served as Speaker of the Massachusetts House of Representatives from 2009 to 2020, having succeeded Salvatore DiMasi, who resigned due to allegations of an ethics violation.

[8] Prior to becoming the Speaker of the House, DeLeo had created a reputation for himself as a "consensus-builder", someone who strived to prevent "major flareups while crafting the budget".

[8] In early 2008, both DeLeo and John H. Rogers put themselves forward as candidates if the state house speakership, held by legally embattled lawmaker Salvatore DiMasi, became vacant.

[10] In April 2011, DeLeo led a vote to remove the health-care related collective bargaining rights of Massachusetts police officers, firefighters, teachers, and other municipal employees.

[11] During the 2014 corruption trial of former probation commissioner John O'Brien, prosecutors alleged that DeLeo had participated in the job-trading as a means of getting elected Speaker.

[14] Towards the end of 2009, DeLeo began to publicly support casinos as a way to increase revenues, and minimize the effects of the economic downturn.

DeLeo added that the legislation would add jobs and part of the revenue would be put aside for capital investments for Massachusetts businesses.

DeLeo retorted that his plan for expanded gaming was Massachusetts' best way to deal with the revenue shortfalls, and lack of jobs.

[18] At this point, a number of groups opposed to the expanded gaming bill had gained a voice on the state level and the whole process began to lose steam.

Patrick had rejected the measure, and with the end of the full session and the majority of the Legislature on summer break it became apparent that the bill would not survive.