He is the vocalist, pianist and primary lyricist for the bands Something Corporate and main songwriter for Jack's Mannequin and performs solo both under his own name as well as his moniker, Andrew McMahon in the Wilderness.

McMahon recalls that while he was in fourth grade, they briefly stayed in California to support his mother's family after the loss of her brother.

"[2] McMahon started his first band, Left Here, with his high school friends and future Something Corporate bandmates Kevin "Clutch" Page on bass and Brian Ireland on drums in 1997.

Joined by rhythm guitarist Reuben Hernandez (who was later replaced by William Tell), the quintet formed the piano rock band Something Corporate in 1998.

McMahon's vocals, songwriting skills, and incorporation of the piano earned the album rave reviews and caught the attention of Drive-Thru's distributor MCA (now Geffen).

[4] The initial impulse behind McMahon's solo project Jack's Mannequin was "Locked Doors", a song he recorded in December 2003, which he felt was too different from previous Something Corporate material.

[5] The idea seemed to be off the table until, in late summer 2004, both McMahon and his bandmates were exhausted from months of touring and decided to take a break.

Touring musicians backing Andrew McMahon during these shows included Jack's Mannequin alum Jay McMillian and Mikey "The Kid" Wagner, joined by Joe Ballaro, Zac Clark, and Jeremy Hatcher.

[9] On April 30, 2013, McMahon released The Pop Underground EP, produced by Mark Williams and Tony Hoffer, followed by an appearance on O.A.R.

In January 2013, McMahon was listed as one of the new songwriters for the second season of the NBC series Smash, signifying his first time writing for musical theatre.

"I Heard Your Voice in a Dream" was met with critical acclaim, being nominated for an Emmy Award for Outstanding Music and Lyrics and has sold 10,000 digital downloads as of April 3, 2013.

[12] On October 15, 2013, New York City venue 54 Below announced plans to stage Smash's fictional musical Hit List in concert format.

Special guests for the show included Bobby "Raw" Anderson, formerly of Something Corporate and Jack's Mannequin, now performing under the name Bob Oxblood.

McMahon embarked on a North American tour in early 2019 in support of the album, with opening acts Flor and Grizfolk.

[37] Morgan Paros, previously of Hunter Hunted, was announced as a new member of the Wilderness line up, and made her performing debut with the band on July 10, 2020.

Through your patronage, the creative team you will help me to empower will be working hard alongside me to provide you with an experience that is constantly evolving — one that reflects where I’ve been and where I’m going and the community that has made it all possible.

[42] On December 3, 2021, Rage Against the Machine's guitarist Tom Morello released his album The Atlas Underground Flood, which features McMahon on the single, "The Maze".

[44] In early April 2022, McMahon and Dashboard Confessional announced the Hello Gone Days co-headlining tour, to kick off on July 31 and last through September 7.

[45] Morgan Paros was not able to take part in the tour due to prior commitments with Ashe, so Zac Clark subbed in.

As part of the show, a surprise Something Corporate reunion was staged, where McMahon, Kevin Page, Brian Ireland, Josh Parrington, and William Tell played a 5-song set.

Additional acts scheduled to join are The Academy Is..., MisterWives, Ruston Kelly, Jukebox the Ghost, Cartel, Augustana, Wildermiss, Hunter DeBlanc, Zac Clark, Bob Oxblood, and Bikelock.

[54] In July 2006, McMahon founded a nonprofit charity, entitled The Dear Jack Foundation, to raise funds for cancer research.

The organization's primary beneficiaries are the Pediatric Cancer Research Foundation, the Leukemia and Lymphoma Society and the regents of the University of California, Los Angeles.

[58] After a medical examination in connection with a relentless case of laryngitis, McMahon was admitted to a hospital in New York City, where he was diagnosed with acute lymphoblastic leukemia on June 1, 2005, the same day he finished recording Everything in Transit.

[60] Over the following couple of months, McMahon received various types of treatment, all the while updating his blog to keep his fans informed on the progress of his condition.

37 on the Billboard 200 with over 22,000 copies scanned within its first week, as well as the day he received a stem cell transplant, with his sister Katie McMahon serving as the donor.

[61] On December 2, 2005, McMahon celebrated the 100-day anniversary of his stem cell transplant by playing his first concert in six months: a private invite-only show in a small venue in Los Angeles, California.

His first public appearance followed ten days later at "Gimme Shelter '05", an acoustic cancer benefit concert at the Roxy in Los Angeles, California.

[63] A documentary entitled Dear Jack was released on October 8, 2009, on DVD by Warner Bros, and was shown at theatrical screenings in New York, Chicago, and Los Angeles.

[64] The film, which chronicles McMahon's struggle with leukemia, features self-recorded footage in the hospital and is narrated by his friend Tommy Lee.