[5] After high school, the Cleveland Indians of Major League Baseball (MLB) offered Eyre a free agent contract, which he turned down in order to pursue a junior college career.

[7] The Texas Rangers selected Eyre in the ninth round of the 1991 MLB draft, but it was not immediately clear if he would sign with the team or if he would play for another year at Southern Idaho.

[9] Eyre made his professional baseball debut in 1992, playing the whole season with the Rookie-level Butte Copper Kings of the Pioneer League.

With a 5–2 record and 2.76 ERA in his first nine starts with the Class A Charleston Rainbows, the director of the Rangers' farm system, Marty Scott, referred to Eyre as "one of the top left-handers in the organization".

The Rangers, still concerned about his slender frame, devised an exercise regimen for Eyre to build muscle mass and upper body strength during the offseason.

[13] His season with the Class A South Bend Silver Hawks came to a premature end that August after suffering a torn ligament in his arm during a game.

[10] Eyre started the 1997 season in Birmingham once again, going 13–5 before receiving his first major league call-up on August 1 as a replacement for Wilson Alvarez, who had been traded to the San Francisco Giants.

[18][19] Eyre, who needed directions from a local cameraman to find the White Sox clubhouse before the game,[20] allowed six runs and six hits in the first 4+1⁄3 innings of a 9–1 loss to the Angels.

[21] Unlike fellow call-up Carlos Castillo, who spent the remainder of the season in the Chicago bullpen, Eyre remained part of an unusually young starting rotation for the White Sox through the end of the year.

[23] That Eyre was not sent back down to the minor leagues after his MLB debut gave him hope that he would be a permanent fixture in the White Sox' 1998 starting rotation.

[24] New manager Jerry Manuel decided to open the season with an inexpensive, young group of pitchers that included Eyre, Baldwin, Bere, Mike Sirotka, and Jaime Navarro.

Eyre suspected that the reason for the demotion had less to do with his own performance and more with the overcrowded bullpen, telling reporters, "When you only pitch four innings in a month, something's got to be wrong.

[10] On November 8, 2000, the White Sox traded Eyre to the Toronto Blue Jays in exchange for pitching prospect Gary Glover.

[37] His new teammates began to notice Eyre's constant fidgeting on the mound during the 2001 season, and the team therapist suggested that he may have attention deficit hyperactivity disorder (ADHD).

Eyre has noted that Lou Piniella could not remember his name for the longest time and called him "Stevie" for a while, jokingly, even after he learned Scott's real name.

"[citation needed] During a game against the Houston Astros on September 12, 2007, Eyre left the Cubs’ bullpen, and wandered around Minute Maid Park.

"[45] After his retirement, Eyre began coaching the baseball team at Saint Stephen's Episcopal School in Bradenton, Florida, where his son played as a first baseman and designated hitter.