It's the first time in the history of the space station that a Canadian has assumed control of the giant orbiting space laboratory.
A small change-of-command ceremony that included the playing of "O Canada" took place on Wednesday as the other five astronauts on board gathered around Hadfield.
NASA astronaut Kevin Ford, the outgoing commander, surprised Hadfield when he played the Canadian national anthem over a speaker.
Hadfield said Ford did a "tremendous honour for playing that song for me and my country."
The 53-year-old space veteran also thanked Ford for giving him "the keys to the family car."
"We're gonna put some miles on it, but we'll bring it back in good shape," Hadfield said.
The transfer of command is the start of what's officially designated "Expedition 35."
Rookie Canadian astronaut David Saint-Jacques said the top job in outer space doesn't come easy, adding that it's the highest accolade that an astronaut can receive.
"To be named commander requires an astronaut to have previous flight experience and this is Chris' third mission," he said from Houston. "It's a little bit like a gold medal."
Former astronaut Marc Garneau, who announced Wednesday that he was quitting the federal Liberal leadership race, said he couldn't think of a better-suited Canadian for the task.
"Certainly in the last few months, he's achieved rock star super status," the Liberal MP said from Ottawa.
Garneau, the first Canadian to fly in space in 1984, also visited the space station in November 2000.
"Geez, I wish Twitter had existed when I flew on my last mission, it might have a different outcome today," he joked.
Since Hadfield's arrival at the space station on Dec. 21, 2012, he has gained over 500,000 Twitter followers thanks to the spectacular photos of the world that he has been posting.
During the transfer of command high above the Earth, a member of the ground crew relayed congratulations to Hadfield and also passed along best wishes from the Queen.
In a message on the British Monarchy's official website, the Queen said she was pleased to transmit her personal best wishes "and those of all Canadians" to Hadfield.
"Our thoughts and best wishes are with him and the entire crew, as are our prayers for an eventual safe return to family, friends and fellow Canadians," she said.
The prime minister also lauded Hadfield on Wednesday, saying ever since the country was founded "Canadians have been pushing the boundaries of exploration and discovery, contributing in substantial ways to collective global knowledge."
Harper said that by being named the first Canadian to take charge of the space station, Hadfield "is continuing in that fine tradition of pushing the limits."
Aside from Hadfield, the only other space station commander who wasn't either American or Russian was Frank De Winne of Belgium.
Hadfield is into the third month of his five-month space station visit, which ends in mid-May.