The two agencies, which make up Channel 4's planning roster, pitched in a five-week battle, overseen by Channel 4's marketing director, Polly Cochrane, and organised by the AAR. M&B is the incumbent on Channel 4 and FilmFour, while Naked looks after the E4 channel.
Rufus Radcliffe, the head of marketing at More4 and E4, said: "M&B's strategic thinking and understanding of the More4 viewer, added to a whole raft of creative media solutions, won through."
Jason Gonsalves, a partner at M&B, will lead the More4 account. He would not discuss strategy but said planning was "at a early stage where we can bring the channel alive".
Although no budget has been published for the channel's launch, it will be Channel 4's biggest promotional campaign for for some years. Channel 4's most recent channel launch was E4 in 2000.
M&B will work alongside DDB, which was last week appointed to handle the creative account for the launch of the station (Campaign, 29 April).
More4 is due to hit the screens in October, and will target over-35s with a combination of original programming and hits such as The Sopranos and The West Wing. OMD retains its grip on Channel 4's media buying account.