A Beautiful Lie received positive reviews from music critics, many praising the album for diverging from the sound of the band's previous work.

[2] To promote A Beautiful Lie, Thirty Seconds to Mars included the songs "Battle of One" and "Hunter" (originally performed by Björk) as bonus tracks.

"Golden passes" were also included with three of the special versions of the album that entitled the buyer free entrance and backstage access to any Thirty Seconds to Mars show for the rest of their formation.

The original 2005 release of the album included the hidden track "Praying for a Riot" inside the song "A Modern Myth".

[16] Jon Wiederhorn from Revolver noted that "intensity and passion clearly inform the textural hard rock of A Beautiful Lie," which "boasts echoing riffs, moody bass lines, and strong vocal melodies that evoke a radio-friendly mix of Staind, Nine Inch Nails, U2, and The Cure.

"[4] Jaan Uhelszki of the San Francisco Chronicle described the album as "full of ferocious electronics, overcaffeinated guitar lines and anxious drumming paired with brainy, brittle but emotionally austere lyrics.

"[14] Nylon magazine called it "an album that is digestible without losing the rough-around-the-edges appeal that the band's rapidly expanding fan base crave.

"[9] Kaj Roth from Melodic praised the sonic variety and summarized the record as "an impressive list of anthemic rock songs.

"[11] Davey Boy of Sputnikmusic echoed this sentiment, writing that A Beautiful Lie "works well as an album due to greater variety".

"[5] He found the band "capable enough at shifting from tense quiet verses to piledriving, heavy choruses, but they borrow the worst habits from all their favorite groups, and then assemble them in insufferably earnest fashion, playing clichés as if they were revelations.

"[5] Christian Hoard of Rolling Stone stated, "[d]espite some credible modern-rock tunes, Leto's self-involved myopia guarantees that his band's second disc is long on melodrama.