O'Connell was born in Los Angeles, California, on December 18, 2001. She is the daughter of teacher, actress, and screenwriter Maggie Baird, and construction worker Patrick O'Connell, who worked part-time as an actor, appearing in films like Iron Man. Both her parents are amateur musicians.

While she was homeschooled, her mother taught her and Finneas the basics of songwriting. O'Connell and her brother had worked together on some music, while he had been writing and producing his own songs and performing with his band.

2015–2017: Don't Smile at Me

2018–present: When We All Fall Asleep, Where Do We Go?

Don't Smile at Me Tour (2017)

Where's My Mind Tour

1 by 1 Tour (2018–2019)

When We All Fall Asleep World Tour (2019)

Where Do We Go? World Tour (2020)

Much of the media attention surrounding Eilish has revolved around her style, which consists primarily of baggy, ill-fitting clothing. In 2017, Eilish stated that she likes dressing out of her comfort zone to feel like she grabs the attention of everyone around her. She tries to be "really different from a lot of people" and dresses opposite to what others wear.