BILLIE was born in Los Angeles on December 18, 2001 her parents are Maggie Baird & Patrick O'Connell they were both work at acting she is of Irish and Scottish descent and her parents chosen her middle name "EILISH" from a documentary about Irish conjoined twins Katie and Eilish Holton, her first name "BILLIE" was supposed to be William After her grandfather William Baird but she turned out being a girl so her parents decided to name her Billie, she was homeschooled and was taught the basics of song writing by her parent, she wasn't interested but her brother Finneas inspired her to get into music

Billie is Naturally blonde, she has been dyeing her hair since she was nine, starting with a Manic Panic shades of blue but she prefers it to be black cuz it feels like her, she took dance classes until 2016 then she sadly stopped cuz of growth plate injury after that she focused on recording music

she started playing the ukulele at age six and wrote her first real song at age 11 about the zombie apocalypse inspired by the series "The Walking Dead" for her mother's songwriting class which she disliked but she enjoyed recording the background, she worked on the films Diary of a Wimpy Kid, Ramona and Beezus, and the X-Men series