Joni Mitchell, the revered Canadian singer-songwriter and one of the defining musicians of the 1960s and '70s, surprised an audience in Rhode Island on Sunday when she appeared at the Newport Folk Festival to perform her first full set in about two decades, guitar in hand.

Mitchell, never one for the limelight, has remained largely out of the public eye since having a brain aneurysm in 2015. As she recovered, she made a few brief appearances: In December, she gave a rare public speech as she accepted a Kennedy Center Honor, and in April, made a televised appearance at the Grammys and was honored at a gala for MusiCares, a Grammy-affiliated charity.

But on Sunday, Mitchell, 78, wearing a beret and sunglasses, performed some of her most iconic songs, including "Carey," "Big Yellow Taxi" and "Both Sides Now."

At one point, Mitchell, an electric guitar slung over her shoulder, performed a several-minutes-long solo during "Just Like This Train," as fans whooped and cheered.

"After all she's been through, she returned to the Newport Folk Fest stage after 53 years and I will never forget sitting next to her while she stopped this old world for a while," the singer-songwriter Brandi Carlile, who sang backup for Mitchell during her festival appearance, said in a Tweet.

Having "looked at life from so many sides," Mitchell has come "out of the storm singing like a prophet," she added.

Although Mitchell has limited her appearances in recent years, she has not avoided the headlines.

In January, Mitchell joined Neil Young in boycotting the streaming service Spotify, over its role in giving a platform to Covid-19 vaccine misinformation.

"Irresponsible people are spreading lies that are costing people their lives," Mitchell wrote of the company at the time. She added, "I stand in solidarity with Neil Young and the global scientific and medical communities on this issue."

On Sunday, several musicians, including Carlile, flanked Mitchell onstage, and sang with her. "I will never be over this. I can't even watch it without the tears coming back," Carlile wrote later on Twitter. "Please forgive me."

As Mitchell and Carlile sang "A Case of You" from the influential "Blue" album, released more than 50 years ago, Mitchell sang:

Oh, I could drink a case of you, darling
And I would still be on my feet
Oh, I would still be on my feet.

The crowd roared.