Harvey Haddix Jr. (September 18, 1925 – January 8, 1994) was an American professional baseball pitcher and pitching coach, who played in Major League Baseball (MLB) for the St. Louis Cardinals (1952–1956), Philadelphia Phillies (1956–57), Cincinnati Redlegs (1958), Pittsburgh Pirates (1959–1963), and Baltimore Orioles (1964–65).

A left-hander, Haddix is most notable for pitching 12 perfect innings in a game against the Milwaukee Braves on May 26, 1959; the Pirates lost the game in the 13th inning.

Haddix enjoyed his best season in 1953, pitching for the Cardinals. He compiled a 20–9 record with 163 strikeouts, a 3.06 earned run average (ERA), 19 complete games, and six shutouts. After five-plus seasons with the Cardinals, Haddix was traded to the Phillies. He also pitched for Cincinnati and Pittsburgh, and finished his pitching career as an effective reliever with the Orioles.

Haddix picked up the Game Seven win in the 1960 World Series, pitching in relief when Pirates second baseman Bill Mazeroski's walk-off home run earned Pittsburgh the title.

Haddix was born in Medway, Ohio, located just outside Springfield. He was nicknamed "the Kitten" in St. Louis for his resemblance to Harry "The Cat" Brecheen, a left-hander on the Cardinals during Haddix's rookie campaign.

Haddix took a perfect game into the 13th inning against the Milwaukee Braves on May 26, 1959. He retired 36 consecutive batters in 12 innings, essentially relying on two pitches: fastball and slider. However, Braves pitcher Lew Burdette was also pitching a shutout, which was seriously jeopardized on only three occasions: the 3rd inning, when a Pittsburgh base-running blunder negated three consecutive singles; the 9th, when Pittsburgh finally advanced a runner as far as third base; and the 10th, when Pirates pinch hitter Dick Stuart came within a few feet of a two-run homer.

Burdette was at the plate in the ninth inning when Pirates broadcaster Bob Prince reported the 27th consecutive out on KDKA Radio back to Pittsburgh. "Anything that (partner) Jim Woods and I have witnessed in this season absolutely at this moment pales into insignificance, and we have had some thumpers. Here's the wind-up and the 1-2 pitch to Burdette . . . Fouled off to the right out of play. And Burdette has shortened the grip on that bat and is trying to really hang in there. And don't forget, he's also quite a threat at the long ball. Two men down, last half of the ninth inning, no score. I can't repeat it enough . . . The 1-2 pitch . . . Struck him out swinging! Haddix pitches a perfect nine-inning, no-hit, no-run game . . . A standing ovation! . . . Ladies and gentlemen, Harvey Haddix has just become the (eighth) pitcher in the history in all baseball to pitch a perfect no-hit, no-run, nine-inning ballgame."

A fielding error by third baseman Don Hoak ended the perfect game in the bottom of the 13th, with the leadoff batter for Milwaukee, Félix Mantilla, reaching first base. Mantilla then advanced to second on a sacrifice bunt by Eddie Mathews, which was followed by an intentional walk to Hank Aaron. Joe Adcock then hit an apparent home run, ending the no-hitter and the game.