As the category recognises the artists and songwriters behind a hit track, Mars took the stage with Christopher Brody Brown, James Fauntleroy, Philip Lawrence, Ray Charles McCullough II, Jeremy Reeves, along with Ray Romulus and Jonathan Yip, who are credited as songwriters on "That's What I Like".
It won over Luis Fonsi and Daddy Yankee featuring Justin Bieber's "Despacito", Jay-Z's "4:44", Julia Michaels' "Issues" and Logic featuring Alessia Cara and Khalid's "1-800-273-8255".
Earlier in the night, Mars gave a high-octane colourful performance with Cardi B on their collaborative single "Finesse".
Before the televised ceremony began on Sunday night, Mars was recognised in Best R&B Performance and Song category for "That's What I Like" and Best R&B album for "24K Magic". The album also was named Best Engineered Album, which lauds the work of sound engineers.