John Russell Carnahan is an American politician from the state of Missouri. A member of the Democratic Party, he served as the U.S. representative for Missouri's 3rd congressional district from 2005 to 2013.

Missouri's third congressional district is in the eastern and central portion of the state. It stretches from the southern part of Columbia and the state capital of Jefferson City in the west to St. Charles County and western Jefferson County in the east. The district took its current form in 2023, when Cooper and parts of Boone counties were added to the district, while Franklin and most of Warren counties were instead drawn into the 2nd district. Its current representative is Republican Blaine Luetkemeyer.