Brendan T. Byrne was born 1 April 1924 in West Orange, NJ, the fourth child of Francis A. Byrne (1888–1973) and Genevieve (Brennan) Byrne's five children. Brendan Byrne attended Seton Hall University before leaving to enroll in the Army Air Corps in 1943 and serving in World War II. He was a navigator and received a Distinguished Flying Cross and three Air Medals. After returning from the war, he graduated from Princeton University in 1949 and received his LL.B. from Harvard University in 1951. He worked as an attorney in New Jersey and married Jean Featherly in 1953.

Brendan Byrne's public career began in 1955 when Governor Robert B. Meyner named him Assistant Council for his administration. The next year he was promoted to Executive Secretary, a position he held for three years. In 1959 he was appointed Essex County Prosecutor. While serving in this capacity, Byrne gained recognition for prosecuting dishonest contractors and powerful underworld figures. He was the prosecutor for nine years. From 1968-1970, Byrne served as president of the State Board of Public Utility Commissioners, having been appointed by Governor Richard Hughes. He left this position when he was appointed to the New Jersey State Supreme Court in 1970 by Governor Cahill. In 1971, he handed down a decision that declared the state law on capital punishment unconstitutional. He resigned from the Supreme Court in 1973 to run for governor.

Byrne’s platform in the gubernatorial election of 1973 was based on the slogan “one honest man can make a difference.” Between the years of 1970 and 1973, seventy-eight New Jersey public officials were indicted by federal grand juries, and Watergate was still in the news. Byrne ran on a platform of restoring public confidence in the government after these events. Byrne’s opponent was Republican candidate Charles Sandman, who criticized Byrne throughout the campaign for his reluctance to publicly state his position on controversial issues such as abortion and the environment. Byrne preferred to make his statements in position papers. On November 6, 1973, Brendan T. Byrne won, by over 721,000 votes, an election that Newsweek called the “biggest gubernatorial victory in the state’s history.”

In 1977 Byrne ran for re-election against Republican candidate Raymond H. Bateman. Despite being considered the underdog in the race, Byrne won again by a large majority.

Brendan Byrne’s time as governor created a legacy that includes the Meadowland Sports Complex, development of the casinos of Atlantic City, dedication to the environment exemplified in the Pinelands Preservation Act, and a commitment to improving public education.

After stepping down as governor in 1982, Byrne returned to working as an attorney, co-wrote a column in the Star-Ledger with his gubernatorial successor Thomas Kean, and has taught classes at Princeton University and Rutgers, the State University of New Jersey. He lives in New Jersey with his second wife, Ruthi Zinn.