Dart began his career as a state prosecutor in Cook County. Afterwards he was an Illinois State Senator, having been appointed in 1991 to fill the vacancy caused by the resignation of Senator Jeremiah E. Joyce (D-Chicago). He was then elected and served state representative as a Democrat for Illinois' 28th House District from January 1993 until January 2003, before becoming chief of staff to Cook County Sheriff Michael F. Sheahan.
When Sheahan announced his retirement in 2006, Dart announced his candidacy to succeed Sheahan. Dart won the Democratic primary election on March 21, 2006, defeating Sylvester Baker and Richard Remus by a wide margin, and won the general election in November 2006. On November 2, 2010, Dart faced Republican Frederick Collins in the race for the Cook County Sheriff's office and won handily with 69.37% of the vote. Dart declined to be a candidate in the Chicago mayoral election, 2011. After defeating three Democratic opponents in the 2014 primary election, Dart was unopposed for reelection in the general election of November, 2014.
In October 2008, Dart made national news when he announced that he was suspending all foreclosure evictions in Cook County. The number of such evictions had increased dramatically since 2006 as a result of the national subprime mortgage crisis. Dart stated that many of the people being evicted were renters who had faithfully paid their rent but had not known that their landlord was in financial trouble. He explained that in many cases, mortgage companies had not fulfilled their obligation to identify tenants in the foreclosed properties, and said, "These mortgage companies only see pieces of paper, not people, and don't care [...] who gets hurt along the way ... We're not going to do their jobs for them anymore. We're just not going to evict innocent tenants. It stops today."
The Illinois Bankers Association was critical of Dart, accusing him of "ignoring his legal responsibilities" and of engaging in "vigilantism".
Dart claims he is enforcing an Illinois state law which requires the banks to determine whether the persons resident at an address are actually the persons to whom the foreclosure notice should be served. Time named Dart one of its 100 most influential people for 2009.
In March 2009, Dart filed a lawsuit in federal court against Craigslist, Inc. (09-CV-1385), to close the "erotic services" section of Craigslist. The suit claims that Craigslist is the "largest source of prostitution" This lawsuit was dismissed on October 23, 2009 on the grounds that Craigslist is protected by Section 230 immunity.
Dart holds a J.D. from Loyola University Chicago and a Bachelor's degree in History and General Social Studies from Providence College. He graduated from Mount Carmel High School in Chicago. He and his wife Patricia live in Chicago's Mount Greenwood neighborhood; they have five children.
- U.S. Public Records Index Vol 1 (Provo, UT: Ancestry.com Operations, Inc.), 2010.
- "Loss to Topinka - 2002 State Treasurer General Election Results - Illinois". Uselectionatlas.org. 2007-01-02. Retrieved 2010-02-04.
- Chase, John; Mack, Kristen (October 27, 2010). "Sheriff Tom Dart won't run for Chicago mayor". Chicago Tribune. Retrieved October 28, 2010.
- "Stroger, Jackson call for statewide foreclosure moratorium". Chicago Tribune. 26 October 2008. Retrieved 2009-08-04.
- "Illinois sheriff: No foreclosure evictions on my watch", CNN, October 8, 2008
- "Sheriff Dart explains why he refuses to evict tenants", Chicago Sun-Times, October 9, 2008.
- Judge Abner Mikva (2009-04-30). "Thomas Dart - The 2009 TIME 100". TIME. Retrieved 2010-02-04.
- Dart v. Craigslist, 665 F. Supp. 2d 961 (N.D. Ill. Oct. 20, 2009)
- "Sheriff sues Craigslist as 'largest source' of prostitution". Chicago Breaking News. 2009-03-05. Retrieved 2010-02-04.
- "Court Teaches Cook County Sheriff About Section 230, Dismisses Case Against Craigslist". Techdirt. 2009-10-21. Retrieved 2010-02-04.
- "Mount Carmel Students and Faculty Break the Bank on St. Baldrick's Day". Mount Carmel High School. 2003-09-28. Retrieved 2010-02-04.
- "Sheriff's Biography". Cookcountysheriff.org. Retrieved 2010-02-04.