And before the next election, expected in the fall of 2015, the prime minister will have the opportunity to appoint two and possibly three more justices.
A replacement for Deschamps will be Harper's third appointment to the court in less than a year. The new justice will be from Quebec to meet the legal requirement that at least three judges must be from that province.
Deschamps will step down in August after a decade on the court.
Chief Justice Beverley McLachlin said Deschamps' retirement will be effective on Aug. 7 — or 10 years to the day after she was appointed, and a few months shy of her 60th birthday.
"Justice Deschamps has made a very significant contribution to the Supreme Court and, more broadly, to the administration of justice in Canada," the chief justice said in a statement.
"We will miss her wisdom, intelligence, keen wit and boundless energy. She has been a wonderful colleague and will always be a good friend."
The chief justice also urged a speedy replacement for the departing judge.
"I am certain that the Canadian government will give necessary care and consideration to the prompt appointment of a new justice of the Supreme Court of Canada."
Harper praised the departing justice for her dedication and contributions to the court.
"Her excellent insight, wisdom, intellect and compassion will be sorely missed, he said in a statement.
Her replacement will be a priority, he added.
Harper said the process will begin with consultations with Quebec's attorney general and leading members of the province's legal community. The public can also nominate candidates.
A pool of qualified candidates will be reviewed by a selection panel composed of five MPs, three from the government and one each from the NDP and Liberals.
The panel will review the candidates and provide the prime minister with an unranked short list of three qualified candidates.
The eventual nominee will appear before an ad hoc parliamentary committee to answer questions from MPs.
The process was first used for the appointment of Marshall Rothstein in 2006.
Deschamps said she is looking for new challenges.
"I feel privileged to have been given the opportunity to participate in the work of the court," she said in a statement.
"I will leave behind a group of empathetic, respectful and dedicated judges.
"After 37 years working mostly in courtrooms, including 22 years on the bench, I feel that it is time to explore other ways to be of service to society. There is so much to do, in so many areas."
Two more justices will reach the mandatory retirement age of 75 before the scheduled October 2015 election.
Morris Fish will turn 75 in November 2013 and Louis LeBel hits that milestone in November 2014. Rothstein turns 75 in December 2015, but could choose to leave early so the court won't lose a justice in the middle of a term.
If Harper is still in office and makes all three appointments, he will have named seven of the nine justices.
That would leave McLachlin — appointed to the court by Brian Mulroney and named chief by Jean Chretien — and Rosalie Abella, a Paul Martin appointment, as the only justices not appointed by Harper.
Deschamps was born in Repentigny, Que., on Oct. 2, 1952. She is married to a businessman and has two children.
Deschamps got her law degree from the University of Montreal in 1974 and a master's degree from McGill University in 1983.
She was called to the Quebec bar in 1975 and practised as a trial lawyer, dealing with commercial, family, civil law and criminal cases.
She was appointed to the Quebec Superior Court in 1990, to the Quebec Court of Appeal in 1992 and to the Supreme Court in 2002.
Her departure is the third in less than a year from the Supreme Court. Last fall, Harper named Andromache Karakatsanis and Michael Moldaver to fill vacancies.
His first Supreme Court appointment came just months after the Conservatives formed their first minority government in 2006, when he nominated Rothstein. He also nominated Thomas Cromwell in 2008.
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