It is the first of two albums by the band recorded without guitarist Dave "Brownsound" Baksh since he left a year earlier to focus on Brown Brigade.

In comparison to the heavy metal-inspired punk style of their previous album Chuck (2004), Underclass Hero marked a return to the band’s pop-punk sound.

It received generally mixed reviews from critics, with some praising its songwriting, lyrics and production, while others found it to be too long, melodramatic, and derivative.

[2] Whibley concurred in his memoir, describing the tunes as "forced, distracted, and although unintentional, some of the work was unoriginal and reminiscent of things I had written before.

PopMatters writer Ethan Stewart stated that "The way that Underclass Hero layers pianos, acoustic guitars, vocal harmonies, and ambient synthesizers easily makes it Sum 41’s prettiest-sounding record to date.

[17] In September and October 2007, the band went on a tour of the US with Schoolyard Heroes, which included an appearance at the X96 Big Ass Show radio festival.

[18][19] In November 2007, the band announced that singer/rhythm guitarist Deryck Whibley was suffering from a herniated disc, resulting in all of the remaining shows of the year to be cancelled.

[20] In February and March 2008, the band toured the UK, which was followed by a stint in Canada; both were supported by Die Mannequin and Social Code.

Billboard also reacted positively, saying that "its growth feels genuine and, unlike Sum 41's punk peers, its musical maturation doesn't come at the expense of that all-important snotty 'tude."

[33] Sputnikmusic gave the album a 1 out of 5, saying that it "tries its best to be profound and musically challenging, however its only success is found, without exception, in the tracks which drop the pretense entirely and return to the formula which made the group popular to begin with."

The track "March of the Dogs" faced political backlash due to its radical opposition to then-United States President George W. Bush.