Zimmer began his career in 1949 with the Cambridge Dodgers of the Class-D Eastern Shore League. He then played with the Hornell Dodgers of the Class-D PONY League in 1950, the Elmira Pioneers of the Single-A Eastern League in 1951, the Mobile Bears of the Double-A Southern League in 1952, and the St. Paul Saints of the Triple-A American Association in 1953 and 1954. He made his major league debut with the Brooklyn Dodgers in 1954. Zimmer’s big league career lasted 12 seasons, almost exclusively as a utility infielder. Notably, he played for the 1955 World Series champion Brooklyn Dodgers, and with the 1962 New York Mets, who lost a record 120 games.

Zimmer grew up in Cincinnati, Ohio. His father owned a wholesale fruit and vegetable company. At home plate before a night game in Elmira on August 16, 1951, Zimmer married Soot (Carol Jean Bauerle), whom he had started dating in 10th grade. Until his death in June 2014, they were still married and lived in Seminole, Florida. They had lived in the Tampa Bay Area since the late 1950s.

While with St. Paul in 1953, Zimmer nearly died after being hit in the temple with a pitch. He was not fully conscious for 13 days, during which holes were drilled in his skull to relieve the pressure of swelling. His vision was blurred, he could neither walk nor talk and his weight plunged from 170 to 124. He was told his career was finished at age 22; fortunately for Zimmer, the prognosis proved incorrect and he made it to the major leagues the following year.

In 12 seasons, Zimmer played 1,095 games. He compiled 773 hits, 91 home runs, 352 RBI, 45 stolen bases and a .235 batting average. He played in the World Series with the Dodgers in 1955 and 1959, and was selected to the National League All-Star team in 1961. Although he had a low career batting average, Zimmer was regarded as a fine infielder, willing to fill in at third base, shortstop, and second base. He also caught 33 games in his final season with Washington in 1965.

Zimmer was beaned again in 1956 when a fastball thrown by Cincinnati Reds’ pitcher Hal Jeffcoat broke his cheekbone, but he persevered. Because of these beanings, it has been widely reported that he had a surgically implanted steel plate in his head. This rumor is false, although the holes drilled in the surgeries following the 1953 beanball were later filled with four tantalum metal corkscrew-shaped “buttons.”

In the major leagues, Zimmer remained with the Los Angeles Dodgers after their move west in 1958. In 1960, the Dodgers traded Zimmer to the Chicago Cubs for Johnny Goryl, Ron Perranoski, Lee Handley and $25,000. After the 1961 season, the expansion New York Mets chose Zimmer from the Cubs as the fifth pick in the premium phase of the 1961 Major League Baseball expansion draft, costing the Mets $125,000. In May 1962, the Mets traded Zimmer to the Cincinnati Reds for Cliff Cook and Bob Miller. He returned briefly to the Dodgers in 1963, when the Reds traded him to the Dodgers for Scott Breeden. The Washington Senators purchased Zimmer from the Dodgers in June 1963. The Senators released Zimmer after the 1965 season, and he played for the Toei Flyers of Nippon Professional Baseball in 1966.

Zimmer served as a player-manager for the Cincinnati Reds with the Double-A Knoxville Smokies and Triple-A Buffalo Bisons in 1967. Zimmer ended his playing career after the 1967 season, and he managed the Triple-A Indianapolis Indians in 1968. In 1969, he left the Reds’ organization for the expansion San Diego Padres, piloting the Class-A Key West Padres before moving up to the Triple-A Salt Lake City Bees in 1970.

In 1971, he joined the Montreal Expos as third-base coach, working under former Dodger Gene Mauch. He spent a year with Mauch, then returned to the Padres to take up a similar post for 1972. But after only 11 games, he was asked to replace Preston Gómez as San Diego’s skipper on April 27. The promotion gave Zimmer, now 41, his first managerial job in the major leagues.

Zimmer compiled a 54–88 record for the remainder of 1972, then posted a 60–102 mark in 1973, each season finishing last in the National League West Division. The Padres’ attendance woes caused the team’s founding majority owner, C. Arnholdt Smith, to sell the club amidst rumors it might move to Washington, D.C. When new owner Ray Kroc bought the team, Zimmer and most of his coaching staff were dismissed.

The 1976 Red Sox never got on track under Johnson who was replaced by Zimmer as manager on July 19. He led them to a winning record, but a disappointing third-place finish in the AL East. The Red Sox would win more than 90 games in each of Zimmer’s three full seasons (1977–1979) as manager, only the second time they had pulled off this feat since World War I. His 1978 team won 99 games, still the fourth-best record in franchise history.

After Texas, Zimmer coached three stints with the Yankees (1983, 1986, 1996–2003), then coached for the San Francisco Giants in 1987. He served as third base coach for the Chicago Cubs from 1984 to 1986. Zimmer took over as manager of the Cubs in 1988. In 1989, he managed the Cubs to a division title and was named Manager of the Year. He was fired as Cubs manager during the 1991 season after a slow start. Later, he returned to Boston for one season as a coach (under manager Hobson) in 1992. Overall, Zimmer won 906 Major League games as a manager.

Zimmer was on the first coaching staff of the expansion Colorado Rockies in 1993, and coached until walking out, without telling manager Don Baylor, in the middle of a game in the 1995 season. He was unhappy that Baylor had become close to Art Howe, who was added to the Rockies coaching staff in 1995.

In 1996, he joined the Yankees as their bench coach for their run of four World Series titles. In 1999, Zimmer filled in for manager Joe Torre while he was recuperating from treatment for prostate cancer. Zimmer went 21–15 while guiding the Yankees during Torre’s absence. (This record, however, is credited to Torre’s managerial record.)

Zimmer was involved in a brawl with Pedro Martínez in the 2003 American League Championship Series, when he ran at Martinez and Martinez threw him to the ground. Zimmer accepted responsibility for the altercation and was apologetic to his family and the Yankees organization but maintained that Martínez was “one of the most unprofessional players” he had ever known. He was also once hit by a sharply struck foul ball batted by Yankee second baseman Chuck Knoblauch. The next game, Zimmer wore an army helmet with the word “ZIM” painted on the side and the Yankees logo stenciled on the front, which was given to him by Michael Patti, a Madison Avenue advertising executive. That event led to the installation of railed fencing in front of the dugouts at Yankee Stadium, which eventually became commonplace at all ballparks.

From the 2008 season to his death, Zimmer was one of the last former Brooklyn Dodgers (besides pitchers Don Newcombe and Tommy Lasorda and announcer Vin Scully) still in baseball in some capacity. Zimmer also served as a member of the advisory board of the Baseball Assistance Team, a 501(c)(3) non-profit organization dedicated to helping former Major League, Minor League, and Negro League players through financial and medical difficulties.

In December 2008, Zimmer suffered a stroke, causing loss of speech for a week.

On June 4, 2014, Zimmer died at age 83 in Dunedin, Florida, from heart and kidney problems.

On March 24, 2015 the Rays announced they were retiring number 66 in honor of Zimmer.