Leading the nominees with 14 nods, Swift's lead single "Shake It Off" won the top streaming song. Additionally, the 25-year-old singer bagged the top artist award after edging out fellow nominees like Ariana Grande, One Direction and Katy Perry.
While the British boy band lost the top artist honour to Swift, One Direction who made their first awards show appearance since Zayn Malik left in March came out as winners in other categories like top touring artist and top duo/group.
Smith, who has been recovering from a throat surgery and couldn't attend the event at MGM Grand Garden Arena in Las Vegas, won the top male artist title over Drake and Justin Timberlake among others.
He also beat 5 Seconds of Summer, Hozier and Meghan Trainor for the top new artist trophy.
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Williams, meanwhile, won the prize in the top R&B artist category which featured the likes of Beyonce Knowles and Chris Brown.
His 2014 solo set "G I R L" won top R&B album and his smashing hit "Happy" won top R&B song.
The 2015 Billboard Music Awards was brought to a close with a performance by Kanye West. The rapper played "All Day" off his new album "Swish" after an introduction from her sisters-in-law Kendall Jenner and Kylie Jenner.