It will help the music awards publicise its new look such as a new venue at the Eventim Apollo, Hammersmith, a broader judging panel.
The competition picks out the 12 best albums of the past year. In another change, fans will be able to choose the first six finalists for 2016. The rest are chosen by the judges, as well as an overall winner which will be announced at the awards show in September.
Somethin’ Else’s campaign will begin this month and include a live newsroom to "produce, share and syndicate content to drive engagement across all major platforms".
It is the first time the awards have used an agency to deliver this content.
Giuseppe De Cristofano, head of digital for the BPI, said: "We really want to grow the social presence and reach of the Hyundai Mercury Prize, ensuring music fans can connect with the prize across multiple platforms.
"Somethin’ Else have a huge amount of experience in creating content and building audiences and I’m delighted we’ve been able to secure their services for this year’s event."