"Spotify just got louder," the company annouced on Thursday.
At an accompanying press event in New York, Metallica drummer Lars Ulrich took the stage with Spotify board member Sean Parker, founder of Napster, a file sharing service which Metallica famously sued more than a decade ago.
Despite the band's past concerns about digital music, past rivals Ulrich and Parker were all smiles as Spotify welcomed Metallica's nine studio albums and other material into its growing catalogue of roughly 20 million songs.
"With the kind of global reach that [Spotify] had, we were ready to jump in," Ulrich told reporters.
According to tech news website CNET, the move by Metallica coupled with the high-profile announcement by Spotify, is meant to "send a message" that Spotify is a "potent legal alternative" to illegal filesharing and will likely to boost the service's credibility with other artists.
Spotify CEO Daniel Ek explained that artists who have already added their music to the company's catalogue have so far been paid $500 million, half of which has been paid out in the last nine months.
Ek added that Spotify also has more than one million paying customers in the United States, and 20 million active users globally.
Spotify also aims to make its service more interactive, announcing features, including a new "Follow" function that will let users to see not only what their friends are listening to, but also following the musical tastes of famous people as well as the artists themselves.
"Want to hear Obama's playlist as he prepares for a big speech? Or check out what David Guetta is listening to this week? Now you can," the company said in a statement.
The company is also launching a new "Discover" tab that will feed users new music recommendations, including new releases from artists users follow.
The new features are set to go online in January 2013.