Ultimate Fighting Championship world featherweight champion Conor McGregor will fight Brazil's Rafael dos Anjos for the lightweight title on 5 March.
Ireland's McGregor, 27, won the UFC featherweight belt with a 13-second win over Jose Aldo in December - and is being allowed to keep that title.
He aims to alternate between each weight, fighting for both belts.
The Dos Anjos fight will take place at Las Vegas' MGM Grand, the venue of the Dubliner's win over Aldo.
McGregor wrote on Facebook after the announcement that he will "behead" the Brazilian, who won the title in March 2015.
The other headline fight on the UFC 197 card sees women's bantamweight champion Holly Holm defend her belt against Miesha Tate.
Holm caused a major shock when she beat Ronda Rousey to win the title in November.