With the appointment of Chrystia Freeland as deputy prime minister, Justin Trudeau has resurrected a cabinet position that lay dormant for the past 13 years.

Former prime minister Stephen Harper chose not to have one, and the current prime minister went without for his first term.

"It's an odd position because ... sometimes we have it, sometimes we don't," said Paul Wilson, associate professor at the Clayton H. Riddell Graduate Program in Political Management at Carleton University.

Freeland exited her role as foreign affairs minister to become the new intergovernmental affairs minister and the 10th deputy prime minister. Anne McLellan was the last cabinet minister to hold the deputy PM position, way back when Paul Martin was prime minister.

On Wednesday, following the swearing-in of his cabinet, Trudeau suggested he chose Freeland for this role because he worked "very, very closely and with great success" with her on the NAFTA renegotiation and what he described as "the challenges of the American administration."

"We know that as we move forward on issues that matter right across the country, like energy and the environment and other large issues, we're going to have to engage in a strong and positive way with different orders of government right across the country and I'm very much looking forward to doing that with Chrystia by my side," he said.

But what, exactly, is expected of a deputy prime minister?

"All the portfolios kind of have a chain of command and a kind of a solid understanding," said Sheila Copps, who was deputy prime minister under Jean Chrétien. "But the [deputy prime minister] position really doesn't. Which kind of is why some prime ministers decide to appoint one, some don't."

Then prime minister Brian Mulroney confers with his deputy prime minister Don Mazankowski prior to a cabinet meeting in Montreal. (Paul Chiasson/Canadian Press)

The position itself, according to the Privy Council Office, has no standing in law and does not carry any formal duties or tasks. Unlike the case of the vice presidency in the United States, there is no law in Canada stipulating the deputy prime minister automatically takes over if the prime minister is incapacitated.

While it's an honorary title, deputy prime ministers have in the past played a variety of roles, as determined by the prime minister.

Those roles have included ceremonial functions, defending the prime minister during question period when the PM is absent (and answering questions on the prime minister's behalf) and playing important policy functions.

How much power the position holds, or where that power puts the deputy prime minister in the hierarchy of cabinet ministers, really depends on the prime minister.

"I think it's up to the prime minister, basically. What are the needs?" Wilson said.

In the cabinet's order of precedence, Freeland is now listed as number two, right behind the prime minister.

"That confirms that being named deputy PM moves her up, while otherwise the rest of the order of precedence is determined by date of being sworn in to the Privy Council," Wilson said.

The position was created in 1977 by Justin Trudeau's father, Pierre Trudeau, who made Allan MacEachen Canada's first deputy prime minister.

Robert Bothwell, professor of Canadian history and international relations at the Munk School of Global Affairs and Public Policy, said Pierre Trudeau owed MacEachen and likely was trying to give him a consolation prize after moving him out of foreign affairs (the ministry was called "external affairs" at the time) to make room for Don Jamieson.

"I think MacEachen was a little sore so I think Trudeau just gave him the honorific to show Allan that he really did like and respect him," Bothwell said.

"It was a recognition that Allan was a big bull in the herd and he was important in its own right. I'm sure that he appreciated that. But it didn't give any particular power."

MacEachen's duties included presiding over cabinet meetings at times, Bothwell said.

But other deputy prime ministers had more power, Wilson said.

Sheila Copps says that Jean Chretien was under pressure not to name a deputy prime minister. (Ron Poling/Canadian Press)

Brian Mulroney's deputy prime minister Don Mazankowski, who chaired the government operations committee, was probably one of the most active and influential deputy PMs, Wilson said.

"I know talking to PCs from the period, he basically ran the operations of government. He was the main person on a day-to-day basis who was really bringing everything together."

Generally, the individual who takes on the role of deputy prime minister is a person of seniority who carries a lot of weight in government, Wilson said.

Other past deputy prime ministers include Jean Chrétien (under John Turner), Erik Nielsen (Mulroney), Jean Charest (Kim Campbell), Herb Grey (Chrétien) and John Manley (Chrétien).

Copps said that before she was named deputy, there was a fair bit of pushback from Chretien's inner circle urging him not to appoint anyone.

"To have a deputy prime minister can also be a another point of contact for the prime minister, which isn't necessarily managed through the PMO," she said.

"The fewer points of contact you have that are outside that orbit, the easier it is for you to control the message."

But Copps said Chrétien told her that it was his wife Aline who helped convince him to name a deputy prime minister. She said she was very honoured at the time to be given that role, particularly because of the tremendous amount of pressure the prime minister was under to not name anyone.

"In the end, it's a great honour to represent your country at these events. But at the same time, the job is a lot more difficult than it looks because of the fact that you've become the face of the government on multiple issues," she said. "And it's sometimes challenging."