Liberty Global says the deal with Virgin Media means the company will have a total of 25 million customers in 14 countries.
It is already the largest cable operator in most of its 11 European markets. But the majority of revenue is expected to come from five countries - the UK, Germany, Belgium, Switzerland and the Netherlands.
Liberty Global says it plans to continue investing in Virgin's broadband network.
More top news
Ex-London mayor Ken Livingstone says he is sorry for the "disruption" caused by his comments that Adolf Hitler was a supporter of Zionism.
Kickstarter group asks for public donations to fund replacing Tube ads with pictures of cats
Sheridan Smith won a standing ovation as she returned to the West End stage after claims she was 'drunk' during a performance.