After attending Selah High School and Yakima Valley Community College, Hull attended the University of Portland. As a senior in 2002, he earned All-West Coast Conference second-team honors for the second straight season after leading the league with eight saves. He posted a 2-3 record in 2002 with a 3.64 ERA and 61 strikeouts in 59.1 innings. 
Hull signed with the Los Angeles Dodgers as an undrafted free agent on June 18, 2002. After a brief stint in the Rookie Leagues, Hull pitched for the Vero Beach Dodgers in 2003 and 2004 before being promoted to the Jacksonville Suns during the 2004 season. In 2003, at Vero Beach he went 3-5 with a 2.68 ERA in 31 appearances (14 starts).
He was briefly promoted to the Major League team in May 2007, but was returned to the 51s a few days later without appearing in a single game.
He made his MLB debut on July 24, 2007, against the Houston Astros, working two scoreless innings in relief. On April 7, 2008, he was traded by the Dodgers to the Boston Red Sox for infielder Christian Lara. He was then optioned to the Triple-A Pawtucket Red Sox.