Cahill attended Vista High School in Vista, California.
The Oakland Athletics drafted Cahill in the second round (66th overall) of the 2006 MLB draft.
In his first full season in minor league baseball, with the Kane County Cougars, he went 11–4 with a 2.73 earned run average, 117 strikeouts and ​105 ¹⁄₃ innings pitched over 19 starts to earn a Class A All-Star nod from Baseball America.

Cahill began 2008 with the Stockton Ports of the California League.
He went 5–4 with a 2.78 ERA and 103 strikeouts to earn a California League All star selection and a promotion to AA.
He also represented America in Major League Baseball's Futures Game.

With the RockHounds, Cahill was 6–1 with a 2.19 ERA before shutting it down in order to compete with the United States national baseball team at the 2008 Summer Olympics in Beijing.

Entering the 2009 season, Cahill was ranked 11th among Baseball America's Top 100 Prospects, and made the Athletics starting rotation out of Spring training along with his Olympic teammate Brett Anderson.
 On April 7, 2009, Cahill made his Major League debut against the Los Angeles Angels of Anaheim, going 5 innings, allowing 5 hits, 2 earned runs, striking out 1 and received a no decision.

Cahill came into the 2010 season as a starter for the A's, quickly becoming one of the breakout pitchers of the year.
He put up borderline Cy Young Award-worthy statistics, finishing the season with an 18–8 record and an ERA of 2.97, making it into the Top 5 of lowest ERA in the American League, behind Félix Hernández, Clay Buchholz, and David Price, all three considered among best pitchers in the American League.
His WHIP was also in the Top 5, with 1.11 WHIP.

For the 2011 season, high expectations were set for Cahill.
Cahill began the season as the A's #1 starter.
Cahill did not replicate his 2010 performance, despite logging in 207 innings in 34 starts.
Cahill finished 12–14 with a 4.16 ERA for Oakland.
Cahill attended Vista High School in Vista, California. The Oakland Athletics drafted Cahill in the second round (66th overall) of the 2006 MLB draft. In his first full season in minor league baseball, with the Kane County Cougars, he went 11–4 with a 2.73 earned run average, 117 strikeouts and ​105 ¹⁄₃ innings pitched over 19 starts to earn a Class A All-Star nod from Baseball America.
Cahill began 2008 with the Stockton Ports of the California League. He went 5–4 with a 2.78 ERA and 103 strikeouts to earn a California League All star selection and a promotion to AA. He also represented America in Major League Baseball's Futures Game.
With the RockHounds, Cahill was 6–1 with a 2.19 ERA before shutting it down in order to compete with the United States national baseball team at the 2008 Summer Olympics in Beijing.
Entering the 2009 season, Cahill was ranked 11th among Baseball America's Top 100 Prospects, and made the Athletics starting rotation out of Spring training along with his Olympic teammate Brett Anderson.  On April 7, 2009, Cahill made his Major League debut against the Los Angeles Angels of Anaheim, going 5 innings, allowing 5 hits, 2 earned runs, striking out 1 and received a no decision.
Cahill came into the 2010 season as a starter for the A's, quickly becoming one of the breakout pitchers of the year. He put up borderline Cy Young Award-worthy statistics, finishing the season with an 18–8 record and an ERA of 2.97, making it into the Top 5 of lowest ERA in the American League, behind Félix Hernández, Clay Buchholz, and David Price, all three considered among best pitchers in the American League. His WHIP was also in the Top 5, with 1.11 WHIP.
For the 2011 season, high expectations were set for Cahill. Cahill began the season as the A's #1 starter. Cahill did not replicate his 2010 performance, despite logging in 207 innings in 34 starts. Cahill finished 12–14 with a 4.16 ERA for Oakland.
Trevor Cahill