[3] On the show, a group of teenage girls such as Olivia Bonilla, Brissia Mayagoitia, and others of Latin background competed in a singing competition for the main prize of $50,000 and a record deal.

[14] The judges unanimously agreed to put her through to the semifinals, with Simon Cowell saying "keep your eye on that one" and Paula Abdul predicting that Iraheta would be a "dark horse" in the competition.

[15] Judges Simon Cowell and Randy Jackson declared Iraheta to be "one to watch in this competition"[16][17] after her rendition of Heart's "Alone" during the semifinals.

[18] Iraheta was the top vote-getting female of Group 2 and, along with Kris Allen and Adam Lambert, advanced directly from the semifinals.

"[22] On Top Downloads night, Iraheta performed No Doubt's "Don't Speak" while accompanying herself on the guitar and ended up in the Bottom 3 again.

[23] For her performance during Top 8 week, Iraheta sang Bonnie Raitt's "I Can't Make You Love Me", for which she received much acclaim.

"[25] During the second Top 7 Night (due to the judges' save of Matt Giraud), Iraheta performed a rock-infused version of Donna Summer's "Hot Stuff".

[29] The following week, Iraheta performed a solo version of "Cry Baby" and closed the show with "Slow Ride", a duet with Adam Lambert.

[30] Regarding her performance of "Cry Baby", Cowell remarked that her growth throughout the competition was "staggering", and praised her for her "complete confidence and terrific vocals".

Tour 2009, performing "So What" by Pink, "Cry Baby" by Janis Joplin, "Barracuda" by Heart, and "Slow Ride" (with Adam Lambert) by Foghat.

[37][42] In September 2009, Allison concluded the 50 city tour with her fellow Idol contestants, during which she began recording her debut album, Just like You, under Jive Records, working with Kevin Rudolf, David Hodges, Tommy Henriksen and Max Martin[43] Iraheta's debut album was released December 1, 2009.

The lead single "Friday I'll Be Over U", produced by Max Martin, debuted on October 5, 2009 and was made available through digital distribution on November 3, 2009.

[48] Allison performed her second single "Scars" on American Idol's Season 9 Top 24 results show on February 25, 2010.

[43] Allison and Australian guitarist Orianthi shared opening act duties on the initial North American leg of the tour.

[51] On Orianthi's final appearance on the tour, Iraheta and her band came onstage, playing air guitar and sweeping up with brooms.

[52] For Iraheta's final date on the tour, September 21, 2010 in Puyallup, Washington, Adam Lambert and his dancers covered her with silly string and carried her offstage.

The band consisted of Iraheta (vocals), Matthew Hager (bass, keyboards), David Immerman (guitars) and Valerie Franco (drums).

The band marked a change of musical direction for Iraheta following a hiatus in 2012, a time which she used to "regroup, find herself and rediscover her voice."

On September 25, 2019, after an 8-month silence on social media, Iraheta announced on Facebook that Halo Circus would be disbanding due to her parting ways with Hager both professionally and personally.