Weinberger was born in San Francisco, California in 1917. His parents had been Jewish but by the time Weinberger was born they were not members of any synagoge or church. Weinberger later joined the Episcopalian Church. He had health problems as a boy, but did well in high school and was accepted to Harvard University. While in college, he edited the "Harvard Crimson", the university's student newspaper. He graduated with a law degree in 1941.