The boy band began the celebrations early by picking up the prize for Favorite Band, Duo Or Group - Pop/Rock, and they were back onstage again to collect the final trophy of the night for Artist of the Year, which they also won in 2014.
"Wow, this is absolutely incredible to receive this award now two years in a row," band member Louis Tomlinson said during their acceptance speech. "Thank you so much. This is a testament of how incredible our fans are. You've been great to us this year, so thank you."
Also going home with two prizes each were Nicki Minaj (Favorite Rap/Hip-Hop Artist and Favorite Rap/Hip-Hop Album - The Pinkprint), and The Weeknd (Favorite Male Artist - Soul/R&B and Favorite Soul/R&B Album - Beauty Behind the Madness).
Taylor Swift claimed the most awards of the night with three, including Song of the Year (Blank Space), Favorite Pop/Rock Album (1989), and Favorite Adult Contemporary Artist, but she was not present at the ceremony.
Other winners included Justin Bieber (Collaboration of the Year - Where Are U Now with Skrillex and Diplo), Luke Bryan (Favorite Male Artist - Country), Carrie Underwood (Favorite Female Artist - Country), and Fall Out Boy (Alternative Artist).
Host Jennifer Lopez kicked off the ceremony with a high energy dance routine to some of the year's (15) biggest hits, while memorable sets came from the likes of Coldplay, who made their first AMAs appearance in seven years, Alanis Morrissette and Demi Lovato, who sang the rocker's hit You Oughta Know in recognition of its 20th anniversary release, and Celine Dion, who paid tribute to the victims of the recent Paris terror attacks with classic Edith Piaf song, Hymne a l'amour.
Other performance highlights at Los Angeles' Microsoft Theatre came from The Weeknd, Nick Jonas, Ariana Grande, Underwood, 5 Seconds of Summer and Bieber, who closed out the show with a medley of his new songs, What Do You Mean?, Where Are U Now, and Sorry, as he danced under a waterfall of fake rain on stage.
The full list of winners at the 2015 American Music Awards is:
Artist of the Year: One Direction
New Artist of the Year: Sam Hunt
Song of the Year: Taylor Swift, Blank Space
Collaboration of the Year: Skrillex & Diplo featuring Justin Bieber, Where Are U Now
Favorite Male Artist - Pop/Rock: Ed Sheeran
Favorite Female Artist - Pop/Rock: Ariana Grande
Favorite Band, Duo Or Group - Pop/Rock: One Direction
Favorite Pop/Rock Album: Taylor Swift, 1989
Favorite Male Artist - Country: Luke Bryan
Favorite Female Artist - Country: Carrie Underwood
Favorite Band, Duo Or Group - Country: Florida Georgia Line
Favorite Country Album: Florida Georgia Line, Anything Goes
Favorite Rap/Hip-Hop Artist: Nicki Minaj
Favorite Album - Rap/Hip-Hop: Nicki Minaj, The Pinkprint
Favorite Male Artist - Soul/R&B: The Weeknd
Favorite Female Artist - Soul/R&B: Rihanna
Favorite Soul/R&B Album: The Weeknd, Beauty Behind the Madness
Favorite Alternative Artist: Fall Out Boy
Favorite Latin Artist: Enrique Iglesias
Favorite Adult Contemporary Artist: Taylor Swift
Favorite Contemporary Inspirational Artist: Casting Crowns
Favorite Electronic Dance Music Artist: Calvin Harris
Top Soundtrack: Pitch Perfect 2.