Brock was a native of Chattanooga, where his family owned a well-known candy company. He is a 1949 graduate of McCallie School and a 1953 graduate of Washington and Lee University in Lexington, Virginia, in 1953 and subsequently served in the U.S. Navy until 1956. He then worked in his family's candy business. Brock had been reared as a Democrat, but became a Republican in the 1950s. In 1962, he was elected to Congress from Tennessee's 3rd congressional district, based in Chattanooga. The 3rd had long been the only Democratic outpost in traditionally heavily Republican East Tennessee; indeed, Brock's victory ended 40 years of Democratic control in the district.
Brock served four terms in the House and then won the Republican nomination to face three-term incumbent U.S. Sen. Albert Gore Sr. in 1970, defeating country singer Tex Ritter in the primary. Brock's campaign was successfully able to make an issue of Gore's friendship with the Kennedy family and Gore's voting record, which was somewhat liberal by Southern standards, and defeated him.
While in the Senate, Brock was a darling of the conservative movement but was less than overwhelmingly popular at home; his personality was somewhat distant by the standards of most politicians. He was considered vulnerable in the 1976 election and several prominent Democrats ran in the 1976 Democratic Senate primary for the right to challenge him. The most prominent and best-known name, at least initially, was probably 1970 gubernatorial nominee John Jay Hooker; somewhat surprisingly to most observers, the winner of the primary was Jim Sasser, who had managed Gore's 1970 reelection campaign.
Sasser was able to exploit lingering resentment of the Watergate scandal, which had concluded only about two years earlier. However his most effective campaign strategy was to emphasize how the affluent Brock, through skillful use of the tax code by his accountants, had been able to pay less than $2,000 in income taxes the previous year; an amount considerably less than that paid by many Tennesseans of far more modest means. Sasser was also aided by the popularity of Democratic Presidential candidate Jimmy Carter in Tennessee as he would win the state by a double-digit margin. Although he started with a 30-point lead in polls over Sasser, Brock would lose his re-election bid by a 47%–52% margin.
Prior to his Senate re-election run, Brock was among those considered to replace Nelson Rockefeller as President Gerald Ford's running mate in the 1976 election.
After leaving the Senate, Brock became the new chairman of the Republican National Committee, a position he held from 1977 to 1981. Upon the election of Ronald Reagan as U.S. president, Brock was appointed U.S. Trade Representative, a position he maintained until 1985 when he was made Secretary of Labor.
Brock resigned his cabinet post in late 1987 to serve as the campaign manager for Senator Bob Dole's presidential campaign. Dole, the runner up to Vice President George Bush, was seen as a micro-manager who needed a strong personality like Brock to guide his campaign. Brock's late start in the Fall of 1987 left little time to help find an avenue to cut into Bush's substantial lead in national polls. Additionally, many viewed Brock as an imperious and inadequate manager who badly misspent campaign funds- largely on national headquarters staff- leaving Dole without adequate money for a Super Tuesday media buy. Dole and Brock had a public falling out, and Brock publicly fired two of Dole's favored consultants, ordering them off of the campaign plane. Dole dropped out of the race in late March 1988 after losing key primaries in New Hampshire, the South and Illinois. Brock became a consultant in the Washington, D.C., area. By this point, he had become a legal resident of Maryland. In 1994 he won the Republican U.S. Senate primary in Maryland over future convict Ruthann Aron, but was soundly defeated (41%–59%) in the general election by Democratic incumbent Paul Sarbanes.
Brock is a member of the ReFormers Caucus of Issue One. He is currently a resident of Annapolis, Maryland.