Harrelson was born on D-Day: June 6, 1944. He grew up in Hayward, California, where he attended Sunset High School, graduating in 1962. He married his first wife, Yvonne, on December 17, 1965. They later divorced, and Harrelson married Kim Battaglia in 1975. Bud’s children are Kimberly, Jessica, Timothy, Alexandra, Kassandra, and Troy Joseph. Harrelson was inducted into the Suffolk Sports Hall of Fame on Long Island in the Baseball Category with the Class of 1992. He appeared as himself in a 1999 episode of Everybody Loves Raymond along with several other members of the 1969 Mets. Harrelson resides in Hauppauge, New York. In 2000, he became co-owner, Senior Vice President for Baseball Operations, and first base coach of the Long Island Ducks, an unaffiliated minor league baseball team. Harrelson was diagnosed with Alzheimer’s disease in 2016.

On May 28, 1969, after a five-game losing streak that saw the Mets fall into fourth place in the newly aligned National League East, Jerry Koosman and the San Diego Padres’ Clay Kirby engaged in a pitchers’ duel at Shea Stadium. After nine scoreless innings by Kirby and ten by Koosman, the game was turned over to the bullpens for extra innings. The game finally ended after 11 innings when Harrelson hit a single to drive in Cleon Jones. This led to an 11-game winning streak that brought them back into second place, seven games back of the Chicago Cubs. Before the streak, the Mets’ record was 18-23; they went 82-39 over the rest of the season.

Harrelson had only two hits in the 1969 National League Championship Series against the Atlanta Braves. However, they were a go-ahead triple in the fourth inning of the first game, and an RBI double in game two of the Mets’ three game sweep.

Harrelson anchored the Mets’ infield for 13 seasons, including their 1969 season, and 1973 pennant-winning season. Harrelson was typical of shortstops of his era: a good fielder, but poor hitter. He had a lifetime batting average of .236 and hit a total of seven home runs during his 15-year major league career, but had a lifetime .969 fielding percentage, and won a Gold Glove at his position in 1971. He was a National League All-Star in 1970 and received Most Valuable Player Award consideration despite batting only .243 for the season.

After his retirement, Harrelson managed the Little Falls Mets in 1984 and the Columbia Mets in 1985. When Mets third base coach Bobby Valentine accepted a managerial position with the Texas Rangers part way through the 1985 season, Harrelson replaced him on Davey Johnson’s coaching staff.

In 1986, Harrelson was inducted into the New York Mets Hall of Fame.

During the 1990 season, Harrelson hosted his own radio show called The Bud Harrelson Report in New York on then-Mets flagship station WFAN but ended it prematurely early in the 1991 season because Harrelson felt some of Howie Rose’s questions he posed to him were too negative.