When the office of the prime minister becomes vacant, it is the constitutional role of the governor general to take the initiative to find a successor who would have the confidence of the House of Commons and to commission him or her to form a government.
When a prime minister is defeated or decides to resign from office, he or she indicates his or her intention to resign to the governor general. In the case of a prime minister informing the governor general of his or her wish to retire and to resign from office, the governor general, in accepting the resignation, may seek the prime minister’s advice as to a successor. The governor general then decides who is in the best position to command the confidence of the House of Commons, and invites that person, during a meeting at Rideau Hall, to form a government. If the governor general’s invitation to form a government is accepted, a time and a date are agreed upon for the swearing in of the new ministry. The formal resignation of the outgoing prime minister, which also covers that of his or her ministers, is submitted to the governor general very shortly before the swearing-in of the new prime minister. His Majesty The King is informed by the governor general of the acceptance of the resignation of a prime minister and of the swearing in of a new prime minister and members of the ministry.
The Oath of Office is administered to the prime minister-designate by the clerk of the Privy Council, at the commencement of the swearing‑in ceremony of the new ministry. The governor general, the prime minister and the clerk of the Privy Council then sign the Oath Book. If the prime minister-designate is not a privy councillor (member of the Privy Council), he or she will first take the oaths of Allegiance and of the member of the Privy Council, before the Oath of Office is administered.
The instrument of advice recommending the appointment of members of the ministry is signed by the prime minister and presented to the governor general. The governor general indicates his or her acceptance of the recommendation by countersigning the instrument of advice.
In the case that any ministers retain the portfolio held under the previous administration, they do not need to be re‑sworn. They are presented to the governor general by the prime minister.
Ministers‑designate are then sworn in to the Ministry in an order determined by the prime minister. Throughout our history, this order has varied.
Ministers-designate who are privy councillors and who are changing portfolios or accepting new portfolios subscribe to their respective oath of office in front of the clerk of the Privy Council before being presented to the governor general by the prime minister.
Ministers‑designate who are not already privy councillors subscribe to the Oath of Allegiance, the Oath of the members of the Privy Council, and the Oath of Office, before being presented to the governor general by the prime minister.
If applicable, the same order is followed for ministers of State-designate. Ministers of State, also known as secretaries of State, are ministers appointed to assist other ministers. They are part of the ministry but not of Cabinet; however, the prime minister may decide that they will attend Cabinet Committee meetings.
For additional information, please consult:
House of Commons Procedure and Practice, Second Edition, 2009.
Edited by Audrey O’Brien and Marc Bosc
© House of Commons, 2009
http://www.ourcommons.ca/procedure-book-livre