Photographs of the meeting showed Trudeau holding the Queen's hand in his while also chatting and laughing.
The head of state was not pictured with the walking stick she has been using of late.
The monarch, 95, has been returning to more normal duties after previously suffering mild cold-like symptoms from COVID-19 and cancelling several engagements.Â
She continued light duties ever since announcing she had coronavirus on February 20.
"I can tell you that in my conversation with her this morning she was as insightful and perspicacious as ever, very interested in what is going on, asked me all sorts of questions about Canada," Trudeau told a Downing Street news conference on Monday.
"We had a really useful, for me anyway, conversation about global events, as we always do."
Trudeau is in the United Kingdom to hold talks with Prime Minister Boris Johnson on the international response to Russia's invasion of Ukraine.
The Queen has two high-profile events coming up - the Commonwealth Service at Westminster Abbey on March 14 and then the Duke of Edinburgh's memorial service, also at the Abbey, on March 29.
with reporting from PA
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