William Joseph Brennan (April 25, 1906 - July 24, 1997) was a Supreme Court justice.

He was nominated for the Supreme Court by Dwight Eisenhower in 1956. He held the post until his retirement on July 20, 1990 for health reasons.

With 1,200 opinions, his is second only to William O. Douglass in number of opinions written while a Supreme Court justice.

An outspoken liberal, he was a staunch opponent of the death penalty, and a supporter of abortion rights.