In 1982, Trauma traveled to Los Angeles to perform at the Whisky a Go Go. Among those in attendance were James Hetfield and Lars Ulrich, both members of Metallica, which had formed the previous year. Upon hearing, as Hetfield described it, "this amazing shredding" (which later became "(Anesthesia) Pulling Teeth"), the two went in search of what they thought was an amazing guitar player. When they learned that what they had heard was a bass solo by Burton, they decided to recruit him for their own band. They asked him to replace departed bassist Ron McGovney, and since Burton thought that Trauma was "starting to get a little commercial", he agreed. The idea of having to move to Los Angeles did not sit well with him, and said he would join only if the band would relocate from Los Angeles to his native San Francisco Bay Area. Metallica, eager to have Burton in the band, left their origin of Los Angeles to make a home in El Cerrito, a town located across the bay from San Francisco.
Burton's first recording with Metallica was the Megaforce demo. A demo tape the band had made prior to Burton's joining, No Life 'til Leather, managed to come into the hands of John Zazula, owner of Megaforce Records. The band relocated to Old Bridge, New Jersey and quickly secured a record deal with Zazula's label. Its debut album, Kill 'Em All, features Burton's famous solo piece, "(Anesthesia) Pulling Teeth", which showcased his use of effects, such as a wah-wah pedal (until then the wah-wah pedal had been the near-exclusive domain of six-string guitarists, with the exception of Geezer Butler on Black Sabbath's debut album, and occasionally ultra-progressive bassists such as Chris Squire).
The band's second album, Ride the Lightning, showcased the band's increasing musical growth. Burton's songwriting abilities were growing, and he received credit on six of the album's eight songs. Burton's playing style and use of effects is showcased on two tracks: the chromatic intro to "For Whom the Bell Tolls", and the "lead bass" on "The Call of Ktulu".
The increase of musicianship on Ride the Lightning caught the attention of major record labels. Metallica was signed to Elektra Records, and began working on its third album, Master of Puppets, which is considered by most critics to be a landmark album in both thrash and the whole of metal. Burton is featured heavily on a number of tracks, most notably the instrumental "Orion", which again featured Burton's lead bass playing style. The album also contained Burton's favorite Metallica song "Master of Puppets". Master of Puppets was the band's commercial breakthrough, but it would be Burton's final album with Metallica.
Burton's final performance was in Stockholm, Sweden on September 26, 1986. One of Burton's final performances with the band is available for free to download from Metallica's website.