She attended Loreto Kirribilli in the Sydney suburb of Kirribilli, graduating in 2016.

While in high school, Scanlen was cast in the recurring role of Tabitha Ford on television soap opera Home and Away. Scanlen starred as the titular character in the 2018 short film Grace. She then achieved recognition for her portrayal of Amma Crellin in the HBO psychological thriller miniseries Sharp Objects, in which she stars alongside Amy Adams.

Scanlen was born in Sydney, New South Wales, Australia, and has a fraternal twin sister named Annabel. She learned the piano when she was about 7 years old, but stopped playing when she was thirteen years old. In preparation for her role as Beth March in the 2019 film adaptation of Little Women, she started practising the piano again.

She made her professional theatre debut in Sydney Theatre Company’s 2019 production of Lord of the Flies, directed by Kip Williams. She played the role of Eric for the play’s run. She made her feature film debut as Milla Finlay in Shannon Murphy’s Babyteeth, which premiered in competition at Venice Film Festival. In 2019, she portrayed Beth March in Greta Gerwig’s adaptation of Louisa May Alcott’s novel Little Women, co-starring alongside Saoirse Ronan, Emma Watson, Florence Pugh, Laura Dern, Timothée Chalamet, and Meryl Streep.