He wrote: “Congrats, Joan! Just in time to vote!”
It is unclear why Mitchell has opted to take up dual citizenship at this time in her life.
Two years ago, fronting a Joni Jam at the Hollywood Bowl, she blasted US President Donald Trump and lamented not being in a position to formally have her voice heard.
She said: “F*** Donald Trump. I wish I could vote… I’m a Canadian. I’m one of those lousy immigrants.”
The Big Yellow Taxi hitmaker previously described Los Angeles as her “workplace” and British Columbia, where she has property, as her “heartbeat”.
Earlier this year, Mitchell, who stepped out of the spotlight for some time after suffering a brain aneurysm in 2015, returned to Canada for the first time in “many, many years” to accept a Lifetime Achievement honour at the Juno Awards in Hamilton, Ontario.
Accepting the prize from Prime Minister Mark Carney, she said: “We are so fortunate to have him. I’m living in the States and you know what’s happening there.
“Some years ago – 10 or 12 years ago, I forget how long ago – I had an aneurysm, which changed my life, oddly, for the better.
“My home’s filled up with the most wonderful nurses. I was on the road with men for years and years, now I live with a house full of women, and I have a fantastic therapist [who] goes everywhere with me. So my life has changed for the better out of a catastrophe, like a phoenix who grows a better life.”