Liberty Global has confirmed that it will buy the firm, part of Sir Richard Branson's empire, in a deal worth £10.3bn.
The US cable giant said the agreement will create "the world's leading broadband communications company" with 25 million customers in 14 countries.
Virgin Media is Britain's second biggest pay TV company with almost five million customers. It was formed through the merger of NTL, Telewest and Virgin Mobile in 2006 and is listed in New York.
Liberty Global has pay TV operations around the world and is the largest cable operator in most of its 11 European markets, including Ireland.
It a statement Liberty Global said the stock and cash merger, subject to shareholder approvals, was valued at approximately 23.3bn dollars (£15bn).
The equity value was calculated at approximately 16bn dollars.
Mike Fries, resident and CEO of Liberty Global, said: "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."
Virgin Media CEO Neil Berkett said: "Virgin Media and Liberty Global have a shared ambition, focus on operational excellence and commitment to driving shareholder value. The combined company will be able to grow faster and deliver enhanced returns by capitalising on the exciting opportunities that the digital revolution presents, both in the UK and across Europe."
It is the second time that Liberty Global, which is chaired by billionaire media mogul John Malone, has looked at buying Virgin Media, in which Sir Richard Branson still holds a minority stake.
It means Mr Malone, who is a former News Corporation shareholder, will become a direct rival of Rupert Murdoch's market leading BSkyB.
Mr Malone had previously built up an 18% stake in Mr Murdoch's News Corporation, before Mr Murdoch swapped it for News Corp's interest in US satellite business DirecTV.
Mr Malone, who has said previously he would like to enter the UK market, surprised the City when he did not bid for a stake in BSkyB when the Murdochs were forced to drop their attempts to gain full control of the satellite giant in the wake of the phone hacking scandal.
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