After a couple of years in the Hanshin minor league system, Igawa entered the starting rotation in 2001.

[citation needed] In his first full season as a starter, Igawa went 9–13 for the last-placed Tigers, but finished with a Central League second-best 2.67 ERA, behind only Chunichi's Shigeki Noguchi.

[5] On November 29, 2006, it was announced that the New York Yankees were the highest bidders at $26,000,194, with the last three digits representing his strikeout total for the 2006 season.

[9] On April 7, 2007, he made his major league debut, allowing seven earned runs in five innings, but received a "no decision" because of Alex Rodriguez's walk-off grand slam.

Igawa came to prominence in a game on April 28, in which starting pitcher Jeff Karstens left in the first inning after suffering a broken leg on a liner back to the mound.

Igawa came in from the bullpen and pitched six innings of scoreless relief, allowing only two hits and striking out six batters before enjoying a standing ovation on his way to the dugout.

[14] Igawa apparently made progress in mechanics and location at Tampa, and was subsequently called up to pitch for the Triple-A Scranton/Wilkes Barre Yankees.

Igawa made his return start against the San Francisco Giants on June 22, 2007, allowing two earned runs in 4.2 innings.

He was claimed on waivers by the San Diego Padres in August 2007,[16][17] but the Yankees pulled him back without making a trade.

[24] In 2009, Igawa was invited to Spring training as a non-roster invitee, the only Yankee with a guaranteed contract in that position.

[27] On July 27, 2009, Igawa set a Scranton/Wilkes-Barre franchise record for most career wins, with a 2–1 victory over the Columbus Clippers.

The Orix Buffaloes of NPB signed Igawa to a two-year contract worth ¥200M prior to the 2012 season.

[35] Igawa also throws a changeup, which hovers in the 78–81 mph range, and a slider, which he uses primarily against left-handed batters.

[35] Igawa is also known for his unique follow-through, in which he throws his left leg into the air and return his pitching arm to a high position.