The attack was savage even by the standards of Mulroney, a man well known for his strong language and dislike of Trudeau.
Mulroney, the 68-year-old Conservative who ruled Canada from 1984 to 1993, made the comments in a memoir due out next Monday as well as a television interview due to be shown on Sunday. The Ottawa Sun newspaper published extracts on Thursday.
Trudeau, a Liberal, who was prime minister for a total of 15 years between 1968 and 1984, is best known for his colorful personal life and for a wide number of social and constitutional reforms.
Although by no means everyone supported or even liked him, polls show Trudeau is regarded as one of Canada's most important prime ministers. He died in 2000.
Mulroney noted that Trudeau had not volunteered to fight during World War Two and said he had also made speeches in which he minimized the Nazi threat.
Mulroney wrote that Trudeau was
Mulroney has long complained that Canadians do not give him enough credit for his achievements, which include the creation of a North American free trade zone.
Trudeau's sons declined to comment on the attack. Liberal leader Stephane Dion said he regretted the remarks and questioned whether they were designed to sell books.
Mulroney blames Trudeau for the failure of the Meech Lake accord, which was designed to end wrangling about national unity by offering constitutional concessions to French-speaking Quebec. Trudeau opposed Meech and described Mulroney as a weakling and a bungler who should have refused to deal with the "snivelers" demanding more rights for Quebec.
The accord died in 1990, triggering an upsurge in Quebec separatist sentiment that almost broke apart Canada.
"'Bunglers', 'cowards', 'snivelers' -- Trudeau knew whereof he spoke," wrote Mulroney, whose reputation is still decidedly mixed despite the passage of time.
He is embroiled in a legal battle with German-born arms dealer Karlheinz Schreiber, who says he paid Mulroney C$300,000 ($285,000) after he left office as part of a business deal. And in 2005, a book based on a series of taped recordings with Mulroney showed him to be vain, spiteful and foul-mouthed.