A young American woman with terminal cancer has committed suicide, following promises to do so that had triggered shock and controversy over the right to die.

Brittany Maynard, a 29-year-old brain cancer sufferer, made headlines earlier this month when a video of her making her suicide threat went viral and was seen by millions of web users.

"Goodbye to all my dear friends and family that I love. Today is the day I have chosen to pass away with dignity in the face of my terminal illness, this terrible brain cancer that has taken so much from me... but would have taken so much more," she wrote in a message circulated widely on social media.

"The world is a beautiful place, travel has been my greatest teacher, my close friends and folks are the greatest givers. I even have a ring of support around my bed as I type... Goodbye world. Spread good energy. Pay it forward!"

Sean Crowley, spokesman for Compassion & Choices, an end-of-life activist group that supported Maynard, said she died peacefully in her home on November 1.

"Brittany has died, but her love of life and nature, her passion and spirit endure," the organization's president, Barbara Coombs Lee, added.

"In Brittany's memory, do what matters most. And tell those you love how much they matter to you. We will work to carry on her legacy of bringing end-of-life choice to all Americans."

In January, Maynard was given six months to live and told her death would be painful because of the aggressive nature of her cancer.

She had been trying for a first child with her husband Dan Diaz at the time, but gave up due to her disease.

Maynard and her husband, who had just married when she began having severe headaches, moved from their home in California to Oregon, one of a handful of US states with a "right-to-die" law.

A doctor could therefore prescribe her the medication she needs to end her own life, surrounded by her family in the bedroom she shares with her husband.

On Thursday, she had released a new video in which she said she might temporarily delay her appointment with a self-administered cocktail of potentially deadly drugs.

But the delay was a short one.

Her story has made headlines around the world, and she was featured on the cover of last week's People magazine in the United States.

Maynard has in recent weeks and months been working to tick off items on a "bucket list" of what she wants to do before she dies -- including traveling to the Grand Canyon last week.