He was selected by the Los Angeles Dodgers in the 1st round of the 2007 MLB Draft out of Midland Christian High School. As a senior at Midland, Withrow was 8–1 with a 1.32 ERA and 90 strikeouts. He missed most of the 2008 season with an assortment of injuries and then spent the majority of 2009 with the Inland Empire 66ers, where he was 6–6 with a 4.69 ERA in 19 appearances. He was rated as the Dodgers #2 prospect by the MLB Network before the 2010 season and was assigned by the Dodgers to the Double-A Chattanooga Lookouts. He started 27 games for the Lookouts, with a record of 4–9 and a 5.97 ERA. In 2011 with the Lookouts, he started 25 games and finished 6–6 with a 4.20 ERA. He was added to the 40-man roster after the season to protect him from the Rule 5 Draft. In 2012, after 7 starts, the Dodgers decided to turn him into a relief pitcher. He finished the season with a 3–3 record and 4.65 ERA in 22 games. The Dodgers promoted him to the AAA Albuquerque Isotopes to start 2013. He was called up to the Dodgers for the first time on June 11, 2013 and made his debut the following night in relief against the Arizona Diamondbacks. In of an inning, he allowed 3 hits, walked one and struck out one. In 26 games for the Dodgers he was 3–0 with a 2.60 ERA and also picked up his first save on September 3 against the Colorado Rockies. Withrow began 2014 in the Dodgers bullpen and pitched 21 innings in 20 games. He had a 2.95 ERA and 28 strikeouts but he also walked 18. However, on May 30, he was diagnosed with a torn ligament in his right elbow, requiring Tommy John surgery, which shut him down for the rest of the season. He remained on the 60-day disabled list at the start of the 2015 season.
Atlanta Braves
On May 27, 2015, he was traded to the Atlanta Braves in exchange for Alberto Callaspo, Eric Stults, Ian Thomas and Juan Jaime. Though Withrow was eligible for arbitration, he and the Braves agreed to a one-year contract for the 2016 season worth $610,000 on January 14. Withrow was invited to spring training, but did not make the team, instead starting the 2016 season with the Triple A Gwinnett Braves. Withrow received his first callup of the season on April 10, and returned to the minors on May 1. On May 26, the Braves recalled Withrow. He pitched at the major league level until August 6, when he was placed on the disabled list with right elbow inflammation. Withrow returned and made six appearances during the first half of September. At the end of the season, he became a free agent.
On January 7, 2017, Withrow signed a minor league contract with the Kansas City Royals that included an invitation to spring training. He spent the entire season on the disabled list and elected free agency on November 6, 2017.
