He was 82.
Lynch died of complications from a previous battle with prostate cancer, the Pittsburgh Post-Gazette reported.
He had a .277 career batting average and 115 home runs in 1,184 career games.
Lynch played for the Pirates 1954-56 before being traded to the Reds, where he played 1957-63. He returned to the Pirates in a trade in 1963 and played until 1966. He was released by the Pirates after the 1966 season.
Lynch had 116 pinch-hits in his career, ranking 10th on the career list, and retired with 18 pinch-hit home runs, then a record, now the third-highest in history.
In 1988, Lynch was inducted into the Cincinnati Reds Hall of Fame.
After Lynch's major league career, he and former Pirates shortstop Dick Groat were business partners who owned Champion Lakes Golf Course in Bolivar, Pa.
Lynch's wife, Alice Lynch, said he had requested his ashes be sprinkled over the golf course, where he and his wife had spent a week every summer.