The consortium is led by the Canada Pension Plan Investment Board and by funds advised by the European private equity firm BC Partners, which has its headquarters in London.
Altice, which is based in the Netherlands, said in September that it planned to acquire Cablevision for $17.7 billion, including debt, in an effort to strengthen its position in the American pay-television market.
The Canada Pension Plan Investment Board and BC Partners, along with co-investors, will pay about $1 billion for the 30 percent stake, Altice said.
BC Partners and the Canadian pension fund sold a controlling stake in Suddenlink Communications, which is based in St. Louis, in May that valued the provider of cable and broadband services at about $9.1 billion.
“This is an attractive opportunity to invest in a sector that we know well,” Shane Feeney, a managing director at the Canada Pension Plan Investment Board, said in a news release.
As part of the deal, the Canada Pension Plan Investment Board and the BC Partners funds will each invest about $400 million for 12 percent stakes in Cablevision apiece, and other investors will buy a 6 percent stake.
The acquisition of the New York-based Cablevision by Altice is expected to close in the first half of 2016 and requires regulatory approval.
Altice, which is controlled by the French billionaire Patrick Drahi, is looking to rapidly expand its presence in the United States after aggressively pursuing deals for cable television and cellphone companies in Europe.
As part of the Cablevision deal, Altice would also acquire the newspapers Newsday and amNewYork, as well as the local television channel News 12 Networks.
The Cablevision deal came as the number of broadband and cable television providers was rapidly shrinking in the United States in a wave of consolidation.