[2] The Philadelphia Phillies selected Biddle in the first round, with the 27th overall pick, of the 2010 Major League Baseball draft.

Although he had committed to attend the University of Oregon,[3] he agreed to a contract with the Phillies on June 10, with a signing bonus of $1.16 million.

[4] In his first season, he amassed a 3–1 win–loss record, 4.32 ERA, 41 strikeouts, and 9 walks in 33+1⁄3 innings pitched for the Gulf Coast League Phillies.

On April 22, 2013, with the Reading Fightin' Phils, Biddle posted 16 strikeouts in a game in Harrisburg against the Senators, breaking the previous record of 13 for his team.

In May of 2014, Biddle was hit by hail during a storm and dealt with headaches as a side effect, forcing him to miss a start for precautionary reasons.

[9] It was later reported to have caused a concussion that Biddle struggled pitching with - in five starts following the incident, he had an 0-5 record and accrued a 9.82 ERA.

[10] Phillies management were uncertain about the severity of the head injury but shut him down for a "mental break" in June.

The next day, he made his Lehigh Valley debut, giving up seven earned runs on five hits and six walks in 2+1⁄3 innings pitched.

[19] Biddle recorded his first major league hit, a RBI double, against the Phillies on April 29, 2018, along with pitching two scoreless innings.

[21] Biddle was traded to the Seattle Mariners along with Arodys Vizcaino in exchange for Anthony Swarzak and cash considerations on May 20, 2019.

[38] He made 8 appearances for the Triple-A Reno Aces, but struggled immensely to a 14.29 ERA with 6 strikeouts in 5.2 innings pitched.

[41] Biddle grew up in Mount Airy with his parents, David and Marion, and his brothers, Sam and Conor.