Liberty Global paid Â£481 million ($824 million) to buy the shares from the Rupert Murdoch-controlled U.K. satcaster BSkyB.
Liberty told ITV and U.K. regulators that it has no intention to make a full takeover bid for the company.
The deal brings to an end a bitter row in the U.K. that started in 2006 when BSkyB boss James Murdoch bought a 17% stake in ITV in order to prevent cable TV group NTL buying the nationwide channel.
News Corp. and BSkyB were blocked by media regulators, and BSkyB was obliged to sell down its stake to 7.5% -- at considerable loss.
NTL later became Virgin Media and was eventually bought by Liberty Global.
"This is an opportunistic and attractive investment for us in our largest cable market. ITV is the leading commercial broadcaster in the U.K. and we're excited to be shareholders," said Mike Fries, Liberty Global's chief executive officer.
Liberty Global intends to finance the acquisition of ITV shares through a combination of a loan linked to a hedging transaction that would be secured by ITV shares and existing liquidity.
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