Thomas Evert Petri (born May 28, 1940) is an American politician who was the U.S. Representative for Wisconsin's 6th congressional district from 1979 to 2015. He is a member of the Republican Party.
Born in Marinette, Wisconsin of German and Norwegian ancestry, he graduated from Goodrich High School in Fond du Lac, Wisconsin. Petri then attended Harvard University, where he received his Bachelor of Arts and Bachelor of Laws degrees. He served as a volunteer with the Peace Corps.
Petri served in the Wisconsin State Senate from 1973 to 1979.
Petri ran for the U.S. Senate in 1974. He won the Republican primary with 85% of the vote. In the general election, incumbent Democrat U.S. Senator Gaylord Nelson defeated Petri 62%–36%. Petri only won five counties in the state. In 1977–78, Petri made a run for governor for Wisconsin, but lost his party's convention nomination to Bob Kasten in 1978. Kasten lost the Republican primary to Lee S. Dreyfus, who won the general election over incumbent Marty Schreiber.