He was born in Loma Linda, Calif., and attended public schools in South Pasadena and San Marino. He attended Occidental College and California Institute of Technology under the U.S. Navy's V-5 Pilot Program. He graduated from Stanford University in 1950 and Stanford University Law School in 1953.

He served in the U.S. Navy from 1945 to 1947, the U.S. Marine Corps from 1950 to 1952, the U.S. Marine Corps Reserve from 1952 to 1960 and the Ready Reserve from 1960 to 1967.

He was Deputy District Attorney for Alameda County, Calif., from 1953 to 1954 and practiced law in Palo Alto, Calif., from 1955-1967. He was a lecturer on legal ethics at the Santa Clara and Stanford Law Schools from 1964-1967. He was elected as a Republican to the 90th Congress, by special election, to fill the vacancy caused by the death of U.S. Rep. J. Arthur Younger and reelected to the seven succeeding Congresses and served from December 12, 1967 to January 3, 1983. He was not a candidate for reelection in 1982, but was an unsuccessful Republican candidate for nomination to the United States Senate. He taught political science at Santa Clara University in the early 1990s. He was an unsuccessful candidate for the Republican presidential nomination in 1972. For many years he practiced law in Redwood City, California and resided in Woodside, Calif. He recently moved to San Joaquin County in order (as he states on his official campaign site) to run for Congress against incumbent Congressman Richard Pombo of Tracy.

McCloskey was the first Republican Congressman to call for the Impeachment of Former President Richard Nixon after the Watergate Scandal and the Saturday Night Massacre.

One of Pete McCloskey's enduring legacies is his co-authorship of the Endangered Species Act.

In 2004, McCloskey broke with party ranks to endorse John Kerry in his bid to unseat George W. Bush as President of the United States.

In the late 1980s, religious broadcaster Pat Robertson sued Congressman McCloskey and Representative Andy Jacobs for libel. McCloskey, who served with Robertson in Korea, made claims that Robertson was spared combat duty when his powerful father, U.S. Senator Absalom Willis Robertson, intervened on his behalf. Jacobs repeated these statements publicly. During pre-trial depositions, another veteran who had served with Robertson, Paul Brosman, Jr., spoke of rumors during the war that Robertson had been carousing with prostitutes and hassling Korean women. Brosman stated that Robertson himself talked about his exploits with prostitutes. Eventually, Robertson dropped his lawsuit because of scheduling conflicts between court dates and his 1988 presidential campaign, and he was ordered to pay part of McCloskey's court costs. An officer in the Marine Corps, Pete McCloskey won both the Navy Cross and the Silver Star for outstanding service during the Korean War. In the last decade, he wrote the book "The Taking of Hill 610" describing some of his exploits in Korea.

Pete McCloskey gave a featured address to the Holocaust denial group Institute for Historical Review in 2000 , .

In 1989, McCloskey cofounded the Council for the National Interest along with former Congressmen Paul Findley (R-IL).