At Windsor castle, the monarch held an audience with Mr Trudeau on Monday.
Mr Trudeau is in the UK for talks on Vladimir Putin’s war in Ukraine with Prime Minister Boris Johnson and Dutch Prime Minister Mark Rutte.
The smiling Queen, 95, welcomed the Canadian Prime Minister, 50, into her home and shook hands with him.
For the occasion, she wore a blue patterned dress and a string of pearls around her neck.
Her Majesty has a strong bond with Canada and she has visited more than 20 times including a trip as a princess.
Mr Trudeau first met the Queen as a young child in the 1970s through his dad Pierre Trudeau who was one of Canada’s longest-serving Prime Ministers.
Their meeting comes after her Majesty tested positive for Covid on 20 February but it is understood she had mild cold-like symptoms.
It was just days after her son Prince Charles and his wife Camilla caught coronavirus.
At the time, a Buckingham Palace statement said: “Buckingham Palace confirm that The Queen has today tested positive for COVID.
“Her Majesty is experiencing mild cold-like symptoms but expects to continue light duties at Windsor over the coming week.
“She will continue to receive medical attention and will follow all the appropriate guidelines.”
The Queen is the nation’s longest reigning monarch and she reached her remarkable Platinum Jubilee milestone in February.