Brock was a native of Chattanooga, where his family owned a well-known candy company. He graduated from Washington and Lee College 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 raised 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.

Brock served four terms in the House and then won the Republican nomination to face three-term incumbent U.S. Sen. Albert A. Gore Sr. in 1970, defeating country singer Tex Ritter in the primary. Brock's campaign was able successfully 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, he would be defeated by Jim Sasser, who had managed Gore's 1970 reelection campaign. Sasser was able to exploit both lingering resentment of the Watergate scandal, which had concluded only about two years earlier, but his most effective campaign strategy was to emphaisize 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 defeated Brock in November.

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 left public life in 1987 and became a consultant in the Washington, D.C., area. By this point, he had become a legal resident of Maryland. In 1994, he ran against Democratic Senator Paul Sarbanes, but was badly defeated. Brock is currently a resident of Annapolis, Maryland.