Simon is the country's first Indigenous Governor General.
It's a historic first for Canada.
Mary Simon has been sworn in as the country's first Indigenous Governor General.
Earlier this month, she was appointed by Prime Minister Justin Trudeau to take over the role.
Trudeau says Simon's appointment is a big step in the path to reconciliation.
“I am inspired by the historic nature of this moment, as our country continues to come to terms with the difficult realities of our collective past. I know that, as Canada’s first Indigenous Governor General, Her Excellency will devote herself to helping us as we confront these difficult truths together, walk the shared path of reconciliation, and build bridges between all those who call our country home."
Simon, a prominent Inuk leader and former ambassador, will act as the Queen's representative in Canada.
Among the fifty guests at today's swearing-in ceremony are Trudeau and his wife Sophie-Gregoire Trudeau and Minister of Crown-Indigenous Relations Carolyn Bennett.
Just last week, Simon spoke with the Queen for the first time.
A clip of their chat was posted on the Royal Family's Instagram account, with the Queen noting that Simon was "taking over a very important job."
In addition to representing the Queen, Simon will also become the top commander of the Canadian Armed Forces.
Simon is the country's 30th Governor General.