The US-based media company owns a range of international TV and broadband assets including Irish cable operator UPC and British-based content distributor Chellomedia.
Liberty Global will continue to use the Virgin Media brand in the UK.
Mike Fries, Liberty Global's president and CEO, said: "Adding Virgin Media to our large and growing European operations is a natural extension of the value creation strategy we've been successfully using for over seven years.
"Virgin Media will add significant scale and a first-class management team in Europe's largest and most dynamic media and communications market.
"After the deal, roughly 80% of Liberty Global's revenue will come from just five attractive and strong countries - the UK, Germany, Belgium, Switzerland and the Netherlands."
[Images from Virgin Media publicity campaigns featuring Usain Bolt (left) and Stephen Fry (right)]
Virgin Media's CEO Neil Berkett added: "Over the past six years, Virgin Media has transformed the digital experience of millions of customers, catalyzed a deep-rooted change in the UK's digital landscape and delivered impressive growth and returns for our shareholders.
"I'm confident that this deal will help us to build on this legacy."
The deal is subject to approvals from regulators and both companies' shareholders, and is expected to close in the second quarter of this year.