Danielson also wrestled in the Pro Wrestling Guerrilla (PWG) promotion. He made his debut in November 2003 at An Inch Longer Than Average in a losing effort to PWG Champion Frankie Kazarian. He continued to appear in PWG over the next couple of years, winning the PWG World Championship in 2007 and holding it for six months before taking an eleven-month hiatus from the company. He made his return to PWG at the 2008 Battle of Los Angeles tournament. In April 2009, at PWG: One Hundred, Danielson defeated Kenny Omega. The match was notable for its opening, which included Omega and Danielson performing variable tests of strength, including arm wrestling and a thumb war, before singing "John Jacob Jingleheimer Schmidt" along with the crowd. In May, he made another appearance teaming with Paul London, referring to himself as "American Dolphin" in a parodied manner. On September 4 at Guerre Sans Frontières during his last night in PWG, Danielson defeated Chris Hero to win the PWG World Championship for the second time and immediately vacated it afterward.