Peter Joseph Brennan was born in New York City on May 24, 1918, and attended the College of the City of New York. Brennan was a painter's apprentice, later becoming a master painter. During the World War II, he served with the U.S. Naval Reserve.

He was president of the New York City Building and Construction Trades Council (1957-1973), president of the New York Sate Building and Construction Trades Council (1958-1973), and vice-president of the New York State AFL-CIO. Brennan served as secretary of labor for President Richard Nixon from 1973 to 1974 and for President Gerald Ford from 1974 to 1975. He died of lymphatic cancer on October 2, 1996.