McDowell was drafted by the Chicago White Sox in the first round (fifth pick) of the 1987 amateur draft. After only six games in the minor leagues, he made his Major League debut on September 15, 1987. He pitched seven shutout innings against the Minnesota Twins that day to pick up the win. In four starts, he was 3-0 with a 1.93 ERA.
In 1988, he was 5-10 with a 3.97 ERA in 26 starts for the White Sox, but in 1989, while dealing with various injuries he did not pitch in the Majors, making 16 starts for the AAA Vancouver Canadians, where he was 5-6 with a 6.13 ERA.
By the early 1990s, he had established himself as one of the most dependable pitchers in the game, pitching effectively and recording over 250 innings each season from 1991 to 1993, he was selected to the Major League Baseball All-Star Game each of those years. He won 20 games in 1992 and 22 in 1993, when he won the American LeagueCy Young Award and led the White Sox to the postseason (they lost in the 1993 American League Championship Series to the Toronto Blue Jays). From 1988 until 1995, his season ERA was consistently between 3.00 and 4.00, well below the league average. In 1993, he set a modern (post-1950) record by recording a decision in each of his first 27 starts.
After the 1994 season McDowell was traded to the New York Yankees for minor league pitcher Keith Heberling and outfielder Lyle Mouton. McDowell spent one rocky season in New York with the Yankees was 15-10 with a 3.93 ERA in 30 starts. He was perhaps best known for giving the finger to the fans at Yankee Stadium while being booed off the field after getting bombed by the White Sox on July 18, 1995 in the second game of a doubleheader. McDowell was also the pitcher who gave up the walk-off, series-winning hit to Edgar Martínez in Game 5 of the 1995 American League Division Series, scoring Joey Cora and Ken Griffey, Jr. to eliminate the Yankees from the playoffs and send the Seattle Mariners to the American League Championship Series.
McDowell spent 1996-1997 with Cleveland Indians. In 1996 he was 13-9 with a 5.11 ERA in 30 starts but in 1997 he made only 6 starts due to an injury, which may have been made worse by his trying to pitch through it.
He signed as a free agent with the Anaheim Angels in 1998 but was hampered with injuries during his time with the team. He was 5-7 with a 5.68 ERA in 18 starts over two seasons with Anaheim. He was released by the Angels after the 1999 season and retired from baseball.
Even during his baseball career, McDowell played guitar in various groups in the alternative rock genre, usually performing during the baseball off-season.
McDowell's first band, V.I.E.W., which consisted of him and fellow baseball players Lee Plemel and Wayne Edwards, had two albums, "Extendagenda" and "Replace The Mind." The band was formed in 1989 and disbanded in 1992. Their most notable accomplishment was touring with The Smithereens in 1992.
His second band, stickfigure, consisted of McDowell, Michael Hamilton, Mike Mesaros and Frank Funaro. They produced the albums "Just a Thought", "Feedbag", "Ape of the Kings" and "Memonto Mori", before the group disbanded in 2003.
In 2008, musicians Scott McCaughey (of The Minus 5), Steve Wynn, Linda Pitmon, and Peter Buck formed The Baseball Project to pay homage to America 's greatest pastime. Their album Volume 1: Frozen Ropes and Dying Quails contains the song The Yankee Flipper, a tribute to their friend Jack McDowell and a confession that a long night of drinking with the musicians may have led to the infamous finger to the crowd.