Created in 1998 by Jared Leto (vocals and guitar) and his brother, Shannon (drums), 30 Seconds to Mars merely began as a small family project. Things began to speed up quickly, however, and Matt Wachter later joined the band as bassist. After a small revolving door of guitarists (as the band's first two guitarists, Kevin Drake and Solon Bixler, left the band due to issues primarily related to touring), the three auditioned Tomo Milicevic to round out the band's roster. Matt Wachter plays keyboards for the band.

Although Jared Leto is a Hollywood actor, he prefers not to use this information to promote the band; in fact, the band refuses to play at venues that use his fame to promote shows.

30 Seconds to Mars' first — self–titled — album, produced by Bob Ezrin, was released in 2002 to critical acclaim, but only achieved sales of just over 100,000. The band's second album, A Beautiful Lie, was released on August 30, 2005. For this effort, the band traveled (during the course of three years) to four different continents, including five different countries, to perfect their sound and also to allow for Jared's film career. The album was produced by Josh Abraham, whose producing credits also include Orgy, Velvet Revolver, and Linkin Park.

Because A Beautiful Lie was leaked five months before its release, the band decided to include two bonus tracks: "Battle of One" (an original song that was also set to be the album's title track when it was first announced) and "Hunter" (a cover of the Björk song of the same name). To further promote the album, the band also enclosed "golden passes" in a select number of copies, which grant their owners access to any 30 Seconds to Mars concert free of charge, along with backstage access.

On August 31, 2006 the band won the MTV2 Award for "The Kill" at the MTV Video Music Awards, one of two awards they were nominated for. A Beautiful Lie was certified gold by the RIAA in August for distribution of over 500,000 albums.