John Pettit (June 24, 1807 – January 17, 1877) was an American lawyer, jurist, and politician.

Born in Sackets Harbor, New York, he completed preparatory studies and admitted to the bar in 1831.

In 1850 he was a delegate to the Indiana state constitutional convention and a presidential elector on the Democratic ticket in 1852.

He was appointed to the U.S. Senate to fill the vacancy caused by the death of James Whitcomb and served from January 18, 1853, to March 4, 1855; he was an unsuccessful candidate for reelection in 1854.

During the Senate debate on the Kansas-Nebraska Act of 1854, Pettit argued in favor of expanding slavery to Kansas, and famously said that Jefferson's idea (in the United States Declaration of Independence) that "all men are created equal" was not a "self-evident truth" but instead "is nothing more to me than a self-evident lie.