Stéphane Perrault has been nominated by Prime Minister Justin Trudeau as Canada's next chief electoral officer.

But New Democrats are demanding to know why the government put forward a different nominee just three weeks ago.

Marc Mayrand, the previous chief electoral officer, announced in June 2016 that he intended to resign at the end of that year. Perrault, Mayrand's deputy, has been serving as the acting chief electoral officer since Mayrand's departure.

Acting Chief Electoral Officer Stéphane Perrault has been nominated by Prime Minister Justin Trudeau to take over the permanent position. (Elections Canada)

"I am pleased to announce the nomination of Stéphane Perrault as Canada's new Chief Electoral Officer," Trudeau said in a statement. "His experience leading the agency for the last year and a half and administering many by-elections across the country make Mr. Perrault an excellent choice to head Elections Canada."

According to biographical notes distributed by the Prime Minister's Office, Perrault began his civil service career in 1997 when he became a law clerk at the Supreme Court. He subsequently worked for the Department of Justice and the Privy Council Office before beginning at Elections Canada in 2007.

Perrault's nomination must be approved by the House of Commons and Senate. If approved, Perrault would become the seventh chief electoral officer at the federal level since 1920, when the position was created.

Opposition parties typically are informed of a nominee before the nomination is made public. But NDP Leader Jagmeet Singh has written to the prime minister to ask why the government's choice for chief electoral officer apparently changed last month.

"I am writing in response to your letter dated April 27, 2018 regarding your proposal to appoint the next Chief Electoral Officer," Singh writes in a letter co-signed by NDP democratic reform critic Nathan Cullen.

"In your previous letter, dated April 3, 2018, there was a different candidate being considered for the position of Chief Electoral Officer. Please provide an explanation of why they are no longer being considered."

The change of nominee was first reported by the Toronto Star.

Time is tight

In his letter, Singh also criticized the time the government took to settle on Mayrand's replacement.

"It has been 18 months since the position of Chief Electoral Officer has been vacant and Canadians have rightly started questioning the sincerity, as well as the competence of your government to appoint a qualified Chief Electoral Officer," Singh writes. "This delay makes the already challenging task of running the election more difficult."

Singh also demanded that the government provide "the list of candidates who were short-listed for the position, their qualifications, and (that) a list of those who sat on the selection committee be provided to both opposition parties' leaders without delay."

Responding to questions from the NDP in the House of Commons on Tuesday, Treasury Board President Scott Brison cautioned New Democrats to respect the privacy of applicants.

"It's very important ... that we respect the privacy of Canadians who participate in these selection processes," said Brison, who is acting as minister of Democratic Institutions while Karina Gould is on parental leave. "I certainly wish the NDP would respect that same principle, of respecting the privacy of people who participate in these selection processes."