Born in Edgefield County, South Carolina, and a graduate of South Carolina College (now known as the University of South Carolina), Brooks served in the Mexican-American War with the Palmetto Regiment. Brooks once fought a duel with future Texas Senator Louis T. Wigfall and was shot in the hip, forcing him to use a walking cane for the rest of his life. He was elected to the United States Congress in 1853. Although suspicious of political parties, Brooks was officially associated with the Democratic Party.

On May 22, 1856, Brooks beat Senator Charles Sumner with his walking cane in the Senate chamber because of a speech Sumner had made three days previous criticizing President Franklin Pierce and Southerners who sympathized with the pro-slavery violence in Kansas ("Bleeding Kansas"). In particular, Sumner lambasted Brooks' kinsman, Senator Andrew Butler, who was not even in attendance when the speech was read, describing slavery as a harlot, comparing Butler with Don Quixote for embracing it, and mocking Butler for a physical handicap. During the speech Senator Stephen Douglas of Illinois suggested to a colleague that Sumner was going to get himself shot in a duel for the insults.

At first intending to challenge Sumner to a duel, Brooks consulted with fellow South Carolina Rep. Laurence M. Keitt on dueling etiquette. Keitt instructed him that dueling was for gentlemen of equal social standing, and suggested that Sumner occupied a lower social status comparable to a drunkard due to the coarse language he had used during his speech. Thereupon Brooks decided that it was appropriate to sneak up on Sumner and beat him with his thick cane.

Brooks hit Sumner repeatedly; Sumner was trapped by his desk, and was unable to get up or avoid the blows. Brooks continued to beat Sumner even as he lay unconscious on the floor of the Senate until his cane broke.

South Carolinians sent Brooks dozens of brand new canes to replace it. The Richmond Enquirer crowed: "We consider the act good in conception, better in execution, and best of all in consequences. These vulgar abolitionists in the Senate must be lashed into submission."

Brooks survived an expulsion vote in the House but resigned his seat, claiming both that he "meant no disrespect to the Senate of the United States" by attacking Sumner and that he did not intend to kill him, for he would have used a different weapon if he had. His constituents thought of him as a hero and returned him to Congress. Brooks remained in office until his death from the croup in 1857 and is buried in Edgefield, South Carolina.

Sumner was unable to return to duty for more than three years while he recovered. He later became one of the most influential Radical Republicans throughout the conduct of the American Civil War, and on through the early years of Reconstruction.