OTTAWA - Manitoba Premier Gary Doer is set to be Canada's next ambassador to Washington after Prime Minister Stephen Harper reached across party lines and tabbed the New Democrat for the country's most important diplomatic post.

The announcement of Doer as ambassador-designate came less than 24 hours after he surprised observers with the news that he's quitting as premier.

The appointment must be officially accepted by the U.S., but that's considered a formality.

Doer, 61, said he chatted with Harper over two months -- on topics ranging from hockey to politics -- before the prime minister made the offer.

"I was really honoured to have the offer and I really appreciate being the ambassador designate," Doer said at a brief news conference Friday

"This will be the first time in my life I have to be diplomatic ... because I am a designate."

Doer replaces Michael Wilson, a former Progressive Conservative finance minister who has held the job since March 2006.

Opposition politicians welcomed the appointment and the symbolism of Harper ignoring political labels. It was a big turnabout from a day earlier when Harper named Conservative friends to the Senate.

Doer, the longest-serving of the current premiers, is familiar with Canada-U.S. trade issues, especially the "Buy American" provisions in the American stimulus package which have many Canadian exporters worried.

He said a decade as premier made him familiar with the key elements of the file.

"They are the obvious ones: the whole issue of border security, the issues of country of origin legislation and how it's applied in agriculture, the issues of Buy America and how it affects Canadian workers and Canadian communities.

"And certainly the clean energy strategy that I've worked on with different governors and different companies in the United States."

Richard Sigurdson, dean of arts at the University of Manitoba, said Harper's choice of Doer is "brilliant."

Doer amassed a long list of American contacts from his time in office, he said.

Sigurdson added that while Doer and Harper have always seen eye-to-eye on free trade issues, Doer may have a harder time compromising his personal views when it comes to the environment and the military.

"He has been a strong supporter of the Kyoto protocol and he fashions himself as environmentally progressive," Sigurdson said. "The government of Canada doesn't share that view at the moment".

The ambassador-designate, however, made it clear he knows who's boss.

"I'm working for the Canadian prime minister, the Canadian people and the Canadian foreign minister," he said.

Jared Wesley, political studies professor at the University of Manitoba, said Doer has worked closely with American governors on trade issues and energy, which will serve him well in Washington.

"If you ask anyone in intergovernmental affairs for the last 10 years, they'll tell you it's Gary Doer that's been leading the way forging links between western premiers and western governors," Wesley said. "His networks are definitely going to be an advantage".

The prime minister said Doer has "always been an advocate of good and assertive relations with the United States."

"We look forward to seeing you in Washington," Harper said as he introduced the new diplomat at a brief photo opportunity.

Despite his NDP affiliation, Doer was seldom driven by strict ideology while in power. He earned an image as a "Teflon premier," who walked a careful line between cutting small-business taxes and bolstering social programs.

Liberal foreign affairs critic Bob Rae was unstinting in his praise for the "terrific" appointment.

"I've known Premier Doer for 30 years and I can't think of anybody who's better qualified to do the job," Rae said.

"I think it's an imaginative and good appointment and I think it would be churlish of any of us to deny that."

Paul Dewar, foreign affairs critic for the federal NDP, called Doer a pragmatist.

"He does want to get things done so he doesn't stand behind rigid ideology -- which is why he's been successful," the MP said.

Dewar welcomed Harper's decision to ignore party politics.

"I believe he's chosen someone who is more than capable to do the job and who will represent Canada very well," he said. "And it probably doesn't hurt the prime minister that he is not from the Conservative party."

Doer was dean of the current premiers when he unexpectedly announced his departure on Thursday.

Before he entered politics, he was a guard at a youth jail in Winnipeg and head of the Manitoba Government Employees Union.

He served as a cabinet minister in the government of Howard Pawley from 1986 until Pawley's 1988 election defeat. Doer subsequently won the party leadership.

He led the party from the opposition benches for 11 years, before winning the first of three consecutive majority governments in 1999.

Doer is the second former premier in the last five years to get the Washington job. Frank McKenna, New Brunswick premier 1987-97, was named ambassador in 2005.

And the appointment of a New Democrat ambassador by a Conservative premier is nothing new, either. In 1984, Brian Mulroney named Stephen Lewis, a former Ontario NDP leader and scion of one of the party's leading families, as ambassador to the United Nations.