He pitched for his high school baseball team in Silver Creek when they won the Chautauqua County championship in 1912.

In May and June 1914, he put together a streak of eight consecutive victories and became the "phenom" of the PCL,[4] described as the best looking prospect, in the pitching sense, that the Pacific Coast league ever has possessed.

[6] On July 28, 1916, Ehmke was sold by Syracuse to the Detroit Tigers for a price reported to be "the biggest sum ever paid for a pitcher in the State League.

[1] In late July 1917, sportswriter Paul Purman wrote that Ehmke had "bewildering speed, a wizardly assortment of curves and a change of pace which kept the batters off their balance.

[16][17] With no outs and two on in the fifth inning‚ Yankee Ping Bodie fell for the hidden ball trick applied by Tigers' second baseman Ralph Young.

[1] On November 18, 1922, the Tigers traded Ehmke with Babe Herman and Carl Holling to the Boston Red Sox for Del Pratt and Rip Collins.

On September 7 of that year, he no-hit his future team, the Philadelphia Athletics, 4–0, at Shibe Park; not until Mel Parnell in 1956 would another Red Sox pitch a no-hitter.

In that game, Slim Harriss hit a ball to the wall for a double, but was called out for missing first base, preserving the no-hitter.

[21] He followed the performance up with a one-hitter against the Yankees four days later, with the only hit in that game a ground ball that bounced off the third baseman's chest.

[1] Ehmke followed with another strong performance in 1924, finishing among the league leaders in wins (fifth best with 19), ERA (fourth best with 3.46), strikeouts (second best with 119), and innings pitched (first with 315).

[1] On June 15, 1926, the Red Sox traded Ehmke to the Philadelphia Athletics in exchange for Fred Heimach, Slim Harriss, and Baby Doll Jacobson.

He also told Ehmke to scout the Chicago Cubs, who were running away with the National League, on their last East Coast trip of the season—and be ready to pitch Game 1 of the World Series.

[24] Although it was widely thought to be a sentimental move, Mack believed that Ehmke's sidearm style and his mix of control and slow pitches would keep the predominantly right-handed Cubs off balance.

For this reason, Bill James called Mack's decision to start Ehmke "the most brilliant managerial stratagem in the history of baseball.

"[24] At the time, Ehmke also set a record for lowest win total during the regular season by a World Series Game 1 starter.

This record stood until 2006 when St. Louis Cardinals pitcher Anthony Reyes started Game 1 of the 2006 World Series after having gone 5–8 during the regular season.

"[26] By 1925, Ehmke had developed a large canvas tarpaulin product that could cover baseball and football fields when it rained.

[27][30] He had a plant in Detroit, and later Philadelphia, where he manufactured the tarpaulins,[30] later expanding his business to tents, flags and banners in the 1930s,[28] and into defense work, including canvas covers for naval guns, during World War II.