The US media group has entered a definitive agreement to buy the broadcaster and its subsidiary channels, 5* and 5USA, as well as children's brand Milkshake! and digital catch-up TV service Demand 5.
Viacom, which owns channels including Nickelodeon and Comedy Central, will be able to drive its nascent free-to-air TV strategy which in the UK consists of the VIVA channel on Freeview and Freesat.
"The acquisition of Channel 5 accelerates Viacom's strategy in the UK, one of the world's most important and valuable media markets," said Philippe Dauman, chief executive of Viacom. "Channel 5's momentum is indisputable, with impactful programming, increasing popularity and a growing digital platform"."