He has played in Nippon Professional Baseball (NPB) for the Tokyo Yakult Swallows, Fukuoka SoftBank Hawks and in Major League Baseball (MLB) for the New York Mets, Toronto Blue Jays and New York Yankees.

After the 2009 season, Igarashi signed with the New York Mets of MLB as a free agent and pitched for them in 2010 and 2011.

He threw a 6-inning perfect game in ni-gun on September 26, 1998; the contest was cut short due to rain.

Igarashi had a 6-4 win–loss record with a save and a 4.91 earned run average (ERA) in 36 games as a rookie in 1999.

When Takatsu left for the Chicago White Sox, the 24-year-old was handed the Swallows' closer job.

[3] On June 3, he threw a 158 km/h (98 mph) fastball, tying the Nippon Professional Baseball (NPB) record for fastest pitch ever (held by Hideki Irabu and Kazuo Yamaguchi);[4] Igarashi would hit that figure several more times in his career.

On April 6, he teamed with Shugo Fujii and Ishii to strike out 19 batters, a NPB record.

[7] On December 16, 2009, Igarashi agreed to a two-year contract worth $3 million with the New York Mets.

[8] Igarashi debuted for the 2010 New York Mets on April 8, relieving Jonathon Niese in the 7th inning against the Florida Marlins.

He began by walking Cameron Maybin but got Hanley Ramírez to ground into a double play and then got Jorge Cantú on a pop fly.

[9] Igarashi allowed only one run in his first seven MLB appearances, but he was placed on the disabled list on April 21, 2010 after suffering a hamstring injury.

[14] After the season, Igarashi pitched in the Dominican Winter League with the Leones del Escogido.

[15][16] He was signed by the Pittsburgh Pirates to a minor league contract with an invitation to 2012 spring training on December 14, 2011.

[17] After being cut from Major League spring training on March 29, 2012, Igarashi said through Erwin Valencia, the Pirates Physical Therapist and Rehab Coordinator, "[I] was shocked about the news", and "[I] did everything [I] could have done up to this point.

"[18] On March 30, 2012, the Toronto Blue Jays acquired Igarashi from the Pittsburgh Pirates for a player to be named later or cash.

Much of his family lives 200 miles (320 km) south of the location of the 2011 Tōhoku earthquake and tsunami.