Thomas Dale DeLay (; born April 8, 1947) is an American author and retired politician who served as a member of the United States House of Representatives, representing Texas's 22nd congressional district from 1985 until 2006. He was Republican Party House Majority Leader from 2003 to 2005.

DeLay began his career as a politician in 1978 when he was elected to the Texas House of Representatives. In 1988, he was appointed Deputy Minority Whip. In 1994 he helped Newt Gingrich orchestrate the Republican Revolution, which gave the Republicans the victory in the 1994 midterm election and swept Democrats from power in both houses of Congress, putting Republicans in control of the House of Representatives for the first time in forty years. In 1995, he was elected House Majority Whip. With the Republicans in control of both chambers in Congress, DeLay, along with conservative activist Grover Norquist, helped start the K Street Project, an effort to advance Republican ideals. DeLay was elected House Majority Leader after the 2002 midterm elections. DeLay was known as a staunch conservative during his years in Congress.

In 2005, DeLay was indicted on criminal charges of conspiracy to violate election law by campaign money laundering in 2002 by a Travis County grand jury after he waived his rights under the statutes of limitations. In accordance with Republican Caucus rules, DeLay temporarily resigned from his position as House Majority Leader and later, announced that he would not seek to return to the position. He resigned his seat in Congress in June 2006. He was convicted in January 2011 and sentenced to three years in prison but was free on bail while appealing his conviction. The trial court's judgment was overturned by the Austin Court of Appeals, a Texas intermediate appellate court, on September 19, 2013, with a ruling that "the evidence in the case was 'legally insufficient to sustain DeLay's convictions'", and DeLay was formally acquitted. The State of Texas appealed the acquittal to the Texas Court of Criminal Appeals. On October 1, 2014, the Texas Court of Criminal Appeals affirmed the appellate court decision overturning DeLay's conviction.

After leaving Congress, DeLay co-authored, with Stephen Mansfield, a political memoir, No Retreat, No Surrender: One American's Fight. He founded the lobbying firm First Principles, LLC.