Thai authorities initially threatened to deport her after she arrived in Bangkok from Kuwait last weekend.
But armed with a smartphone and hastily opened Twitter account, she forced a U-turn from Thai immigration police who handed her into the care of the UN's refugee agency as the SaveRahaf hashtag bounced across the world.
Qunun alleged that she was abused by her family - who deny the allegations - and rights groups also said she had renounced Islam, risking prosecution in Saudi Arabia.
Rahaf first said she was aiming for Australia where officials had suggested they would give serious consideration to her claim for asylum, which was endorsed as legitimate by the UNHCR on Wednesday.
But late Friday Thailand's immigration police chief said a smiling and cheerful Rahaf was bound for Toronto and had left on a flight after 11:00 pm (1600 GMT).
"She chose Canada... Canada said it will accept her," Thai immigration chief Surachate Hakparn told reporters at Bangkok's main airport.
"She is safe now and has good physical and mental health. She is happy."
Rahaf left from the same airport where her quest for asylum began less than a week ago in a swift-moving process that defied most norms. On Friday afternoon Rahaf posted a final cryptic tweet on her profile saying "I have some good news and some bad news" - shortly after her account was deactivated in response to death threats she had faced, her friends said.
"Rahaf received death threats and for this reason she closed her Twitter account, please save Rahaf life," tweeted supporter @nourahfa313, who has flanked Rahaf's social media campaign with her own updates on Twitter.