Canada's biggest media company had been unable to make interest payments for months on $4 billion Canadian ($3.8 billion) in debt and negotiated several extensions with creditors.
The media giant reached an agreement with a key group of lenders to give them a stake in the restructured company, leaving current shareholders with just 2.3 percent.
Ontario's Superior Court of Justice approved the request to enter bankruptcy protection on Tuesday.
Canwest has been selling pieces of its business to show lenders it's making progress on reworking its operations. It recently sold its majority stake in Australian broadcaster Ten Network Holdings after earlier selling its E!-branded TV stations and the U.S. political magazine The New Republic.
Canwest CEO Leonard Asper and other members of Canwest's founding family have agreed to invest up to $15 million Canadian ($14.2 million) in the restructured company. The company didn't say how much voting control or operational involvement the Aspers would have afterward, but their equity stake will be significantly diminished.
Asper said in a statement that the company believes the restructuring can be implemented in four to six months and, in a memo to employees, that the process is not going to lead to significant job losses.
Business units of the media company that will be filing for creditor protection include the Canwest Television Limited Partnership, which holds Canada's Global Television, as well as MovieTime, DejaView and Fox Sports World, and The National Post Co.
"By working with our major debt holders, we have developed a pre-packaged financial restructuring plan that is intended to minimize business disruption and preserve the value of our operations," Asper said in the memo.
Asper acknowledged in the memo that the company took on too much debt. Canwest accumulated more than $3 billion Canadian ($2.8 billion) in debt when it bought the former Southam newspapers and Canada's National Post newspaper earlier this decade.
"Like all media companies, Canwest's financial performance has been adversely affected by current economic and financial market conditions, including a precipitous and unprecedented decline in advertising revenues. There is no doubt that in this environment, Canwest had too much debt," Asper said in the memo.
The filing does not include specialty channels that Canwest and Goldman Sachs bought from Alliance Atlantis in 2007, nor does it include the subsidiary that owns other newspapers, among which are the Montreal Gazette, the Calgary Herald, the Edmonton Journal and the Vancouver Sun and Province, or the company's online operations including the Canada.com Web portal. The newspaper part of the company is restructuring debt with a different group of bondholders and could also still seek protection.
Last week, a published report said Paul Godfrey, CEO of Canwest's National Post in Toronto, has been approached by private equity funds that want to buy some or all of the Winnipeg media company's papers.
Canwest asserted last week that its newspaper assets aren't officially up for sale at this point, but the report said they're expected to hit the auction block within two months.
Canwest said Tuesday's filing only applies to entities whose businesses account for about 30 percent of the company's revenue.
Shares of the company, which trade on the Toronto Stock Exchange, were halted Tuesday and are expected to be delisted.