1983–1985: Formation and Killing Is My Business

On April 11, 1983, Dave Mustaine was dismissed from Metallica before the band recorded their debut album Kill 'Em All due to substance abuse and personal conflicts with James Hetfield kicking his dog. As Metallica's lead guitarist since 1981, Mustaine had composed some of the group's early songs, including Mechanix, Ride the Lightning, Jump in the Fire and Phantom Lord, and helped hone the band into a tight live unit. Afterward, Mustaine vowed revenge by forming a band that was faster and heavier than Metallica. On the bus trip back to Los Angeles, Mustaine found a pamphlet by California senator Alan Cranston that read: "The arsenal of megadeath can't be rid no matter what the peace treaties come to." The term "Megadeath" stuck with Mustaine and he wrote a song with that title with the spelling slightly changed to Megadeth, which, according to Mustaine, represented the annihilation of power.

1986–1987: Peace Sells... but Who's Buying?

According to Mustaine, Megadeth was under pressure to deliver another successful album: "That sophomore offering is the 'be-all or end-all' of any band. You either go to the next level, or it's the beginning of the nadir." Mustaine composed the music for the album, with the other members adding arrangement ideas.

The album was produced on a $25,000 budget from Combat Records. Dissatisfied with its financial limitations, the band left Combat and signed with Capitol Records. Capitol bought the rights to the album, and hired producer Paul Lani to remix the earlier recordings. Released in late 1986, Peace Sells... but Who's Buying? has clearer production and more sophisticated songwriting. Mustaine wanted to write socially conscious lyrics, unlike mainstream heavy metal bands who sang about "hedonistic pleasures". The album was noted for its political commentary and helped Megadeth expand its fanbase. The title track was the album's second single, and was accompanied by a music video that received regular airplay on MTV.

1988–1989: So Far, So Good... So What!

With a major-label budget, the Paul Lani-produced So Far, So Good... So What! took over five months to record. The production was plagued with problems, partially due to Mustaine's struggle with drug addiction. Mustaine later said: "The production of So Far, So Good... So What! was horrible, mostly due to substances and the priorities we had or didn't have at the time." Mustaine clashed with Lani, beginning with Lani's insistence that the drums be recorded separately from the cymbals, an unheard-of process for rock drummers. Mustaine and Lani became estranged during the mixing, and Lani was replaced by Michael Wagener, who remixed the album.

So Far, So Good... So What! was released in January 1988 and was well received by fans and critics. The album featured a cover version of the Sex Pistols' "Anarchy in the U.K."; Mustaine changed the lyrics, later admitting that he had simply heard them incorrectly. To support the album, Megadeth embarked on a world tour that lasted for nearly eight months. The band (along with Savatage) opened for Dio on their Dream Evil tour and supported Iron Maiden on their Seventh Son of a Seventh Son tour, both in the United States. They also headlined a North American tour with Warlock and Sanctuary (whose debut album Refuge Denied was produced by Mustaine), and a European trek with Testament, Nuclear Assault, Flotsam and Jetsam and Sanctuary.

1990–1991: Rust in Peace

With Mustaine sober, Megadeth continued searching for a new lead guitarist. Guns N' Roses guitarist Slash had been jamming with Mustaine and Ellefson, and although it seemed that he might join Megadeth, he remained with Guns N' Roses. Diamond Darrell of Pantera was offered the job, but the deal fell through after Mustaine refused his request to recruit his brother, Pantera drummer Vinnie Paul, as he had already hired Menza. The offer was also extended to Criss Oliva who also declined as he did not want to leave Savatage. Jeff Loomis, who would later go on to form progressive metal titans Nevermore, also auditioned though Mustaine deemed him too young to join as Loomis was only 18 at the time. Mustaine and Menza played demos of the Rust in Peace album with former guitarist Chris Poland, but he chose not to rejoin the band.

1992–1993: Countdown to Extinction

The music for Megadeth's fifth studio album was written in two different sessions. The first session occurred after the conclusion of the Clash of the Titans tour, while the second session happened in the fall of 1991 following a one-month break. Recording sessions for the album began in January 1992 at Enterprise Studios in Burbank, California. Max Norman was chosen to produce, as the band was pleased with his mixing of Rust in Peace. Megadeth spent nearly four months in the studio with Norman, writing and recording what became the band's most commercially successful album, Countdown to Extinction. The album, whose title was suggested by Menza, features songwriting contributions from each band member. Ellefson explained that the band changed its approach to songwriting for this album, beginning to write more melodic songs.

Released in July 1992, Countdown to Extinction entered the Billboard 200 chart at number two and was certified double platinum in the United States. It received a nomination for Best Metal Performance at the 1993 Grammy Awards, and its title track won a Genesis Award from the Humane Society in 1993 for raising awareness for animal rights issues. Ellefson later said that he and Friedman were disappointed that Megadeth did not win the Grammy: "It was such a bizarre moment, because it was as if the amount of work it had taken to ramp up to that hopeful night was literally gone in a second."

1994–1995: Youthanasia

In early 1994, Megadeth reunited with producer Max Norman for the follow-up to Countdown to Extinction. With three band members living in Arizona, initial work began at Phase Four Studios in Phoenix. A few days into pre-production, problems with Phase Four's equipment forced the band to look for another studio. Mustaine insisted on recording in Arizona, but no suitable recording facility could be found. At Norman's request, the band built its own recording studio in Phoenix in a rented warehouse, later called "Fat Planet in Hangar 18". During the studio's construction, much of the pre-production songwriting and arrangements were done at Vintage Recorders in Phoenix. At Norman's suggestion, the tracks on Youthanasia had a slower tempo than previous albums, at about 120 beats per minute. The band abandoned the progressive approach from its previous albums and focused on stronger vocal melodies and more accessible, radio-friendly arrangements. For the first time, Megadeth wrote and arranged the entire album in the studio, including basic tracks recorded live by the entire band. The album's recording was video recorded and released as Evolver: The Making of Youthanasia in 1995.

1996–1999: Cryptic Writings and Risk

After completing the extensive world tour in support of Youthanasia, Megadeth took time off in most of 1996 and nearly broke up. During this period, Mustaine began work on MD.45, a side project with vocalist Lee Ving of Fear. The majority of the songs on the album were intended for Megadeth, but due to the band almost disbanding, Mustaine decided to use them for MD.45 instead. The duo hired drummer Jimmy DeGrasso, who had played with Alice Cooper on the South American Monsters of Rock tour earlier that year. Marty Friedman built a studio in his new home in Phoenix and completed his fourth solo album, released in April 1996.

In September 1996, Megadeth went to London to work on songs for the next album. The songwriting was closely supervised by new manager Bud Prager, who contributed musical ideas and lyrics; many lyrics and song titles were changed at his request. Regarding Prager's influence, Mustaine later wrote: "I figured maybe this guy [Prager] could help me get that intangible number one record I so badly wanted." The album, recorded in Nashville, was Megadeth's first collaboration with country pop producer Dann Huff, who had met Mustaine in 1990.

2000–2002: The World Needs a Hero, breakup, and hiatus

In January 2000, guitarist Al Pitrelli, formerly of Savatage and the Trans-Siberian Orchestra, became Friedman's replacement. Megadeth returned to the studio in April to work on its ninth studio album. A month into production, the band received an offer to join the Maximum Rock tour with Anthrax and Mötley Crüe. Megadeth put the recording on hold and toured North America during the second quarter of 2000. Early in the tour, Anthrax was removed from the bill, allowing Megadeth to play an extended co-headlining set. The tour, however, suffered from poor ticket sales.

2004–2005: Reformation and The System Has Failed