Pappas pitched seventeen years in Major League Baseball. He had a won-loss record of 209-164 with an ERA of 3.40. He was a three-time All-Star, and had 43 career shutouts. He tossed a no-hitter on September 2, 1972, missing a perfect game when umpire Bruce Froemming squeezed the plate with San Diego Padres outfielder Larry Stahl at the plate calling a close pitch a ball. Pappas retired the next hitter to preserve his no-hitter the only one of his career.
He pitched for the Orioles, Reds, Braves, and closed out his career with the Cubs from 1970-1973. He won 17 games with the Cubs twice in 1971 and 1972. Pappas wasn't just a solid starter, but he was a solid hitting pitcher with 20 career home runs. He was the first pitcher to win over 200 games that didn't have a twenty game winning season. In 1973, Pappas only won 7 games with an ERA of 4.28. In 1974, the Cubs released Pappas prior to the start of the 1974 season.
He was also one of the players sent in trade to the Cincinnati Reds for Hall of Fame outfielder Frank Robinson. He died on April 19, 2016.