"[1] Iha received average grades in high school, and, after a successful two-year stint at a local junior college, he majored in graphic design at Loyola University Chicago before dropping out to dedicate himself to the Smashing Pumpkins.

Iha wrote and sang a number of Smashing Pumpkins' songs, such as: "Blew Away" on Pisces Iscariot, "Bugg Superstar" on Vieuphoria, "Take Me Down" on Mellon Collie and the Infinite Sadness, "...Said Sadly", "Believe", "The Boy", and "The Bells" on The Aeroplane Flies High, "Summer" on the "Perfect" single and "Go" on Machina II/The Friends & Enemies of Modern Music.

He co-wrote with Billy Corgan "I Am One" on Gish, "Soma" and "Mayonaise" on Siamese Dream, "Plume" on Pisces Iscariot and "Farewell and Goodnight" on Mellon Collie and the Infinite Sadness.

[5][6] Iha was often considered the "quiet one" in Smashing Pumpkins, but he was known to engage in ad-libbed jokes and rap sessions at live performances.

His humor was encapsulated in his use of the catchphrase, "I've seen a million faces, and I've rocked them all," originally from the Bon Jovi song "Wanted Dead or Alive".

In 2017, reunion rumors were leaked through various sources, and in 2018, Iha was spotted with Corgan, Chamberlin, and former Smashing Pumpkins guitarist Jeff Schroeder in the studio and at a photo shoot, confirming his return to the band.

Iha made bigger news when he joined the alternative rock supergroup A Perfect Circle in July 2003 in time for their Thirteenth Step club tour.

He collaborated on and produced two tracks with Japanese musician Chara for her 2001 album Madrigal called "Boku ni Utsushite" and "Skirt".

The same year he teamed with Schlesinger again to produce a duet cover of Bobby Darin's "Splish Splash" for the soundtrack to the Wayne Wang film Because of Winn-Dixie.

Iha recorded on the track "The Ballad of Bonnie and Clyde" in a duet with singer Kazu Makino (of Blonde Redhead) on the US edition of the album.

[23] In February 2007, Side-Line announced that Iha delivered a remix for the Ladytron single "Weekend Mixes" out on March 9 via Smoke & Mirrors.

[25] Iha appeared on stage with Swedish band the Sounds, on the season finale of MTV's Bam's Unholy Union in April 2007 and contributed guitar to the song "Seatbacks and Traytables", on Fountains of Wayne's 2007 album Traffic and Weather.

[26][27] A Chicago weekly reported in June 2007 that Iha had been living in New York City for some time, running a recording studio and independent label.

On December 22, 2008, the Swedish band A Camp (the solo project of the Cardigans vocalist Nina Persson) put out a press release announcing that their new album would come out on April 28, 2009, featuring guest appearances by Iha and other musicians.

[28] On February 17, 2009, it was announced that Iha had, together with Taylor Hanson, Fountains of Wayne bassist Adam Schlesinger, and Cheap Trick drummer Bun E. Carlos formed a new band called Tinted Windows.

Shortly thereafter, a picture of Iha with Kelly Pratt and Jon Natchez from the band Beirut was posted on the Web site saying they would be playing horns on the album.

[30] In August 2010, members of A Perfect Circle posted messages to their Twitter accounts telling fans of their return after a 6-year long hiatus.

It was announced that the lineup would consist of Maynard James Keenan, Billy Howerdel, Josh Freese, Matt McJunkins, and Iha.