Newsom was born and raised in the small town of Nevada City, California. Her mother, Christine (née Mueller), is an internist, and her father, William Newsom, is also a doctor. Her parents were "progressive-minded professionals" who previously lived in the Bay Area. Newsom's family includes her brother, Pete, a fellow musician, and sister, Emily, who inspired her song "Emily" (and contributed backing vocals). She is the second cousin, twice removed, of Lieutenant Governor Gavin Newsom of California.
As a child, Newsom was not allowed to watch television or listen to the radio because she was raised by parents whom she described as, "kind of idealists when it came to hoping they could protect us from bad influences, like violent movies, or stupid stuff". She was exposed to music from a young age. Her father played the guitar and her mother was a classically trained pianist who played the hammered dulcimer, the autoharp and conga drums. Newsom attended a Waldorf school where she studied theater and learned to memorize and recite long poems. This skill helps her to remember lyrics while on tour.
At the age of five, Newsom asked her parents if she could play the harp. Her parents eventually agreed to sign her up for harp lessons, but the local harp instructor did not want to take on such a young student and suggested she learn to play the piano first. She did but and later moved on to the harp, which she "loved from the first lesson onward." She first played on a smaller Celtic harps until her parents bought her a full-size pedal harp in the seventh grade. During her teens, she became inseparable from her harp, which she describes as similar to "an artificial limb or a wheelchair. It's almost part of me, but more to the point, it serves a purpose, and if it wasn't there I would wonder what was supposed to fit in its place."
When Newsom was 18, in the middle of her senior year of high school, she decided that she needed "some sort of ritual marker of the end of childhood." Her plan was to camp in the open air for three days and nights, eating little, seeing no one, communing with the great outdoors. Describing her experience, Newsom stated, "I hesitate to speak about it because it sounds so corny, but one of my goals out there was to find a spirit-animal. On the third day, I was kind of delirious. I'd only eaten a little rice. I'd just slept and looked at a river for three days. I was prepared to be visited by my spirit animal – I was just sitting there, saying some sort of prayer, inviting that presence into my life. And then I saw three white wolves charging down at me. I thought maybe I was hallucinating; but I was also prepared to die. But the wolves ran up and started licking my face. Then I remembered that the daughter of the woman who owned the property kept domesticated wolves."
11/7/15 Tivoli Vredenburg Utrecht Netherlands w/ Alasdair Roberts
11/8/15 Salle Gaveau Paris France