She is known for her portrayal of Rosalind "Roz" Walker in the Netflix series Chilling Adventures of Sabrina, Angela in Paper Towns, Anna in When the Bough Breaks, Marie Moreau in Gen V, and various television roles.

[4][1][3] In 2015, Sinclair played Angela in the Jake Schreier-directed comedy-drama film Paper Towns, along with Nat Wolff and Cara Delevingne.

[1][5] In 2016, Sinclair starred as Anna, a surrogate mother, in the thriller film When the Bough Breaks, directed by Jon Cassar.

Sinclair played Chloe in the supernatural horror film Slender Man, which was released in theaters on August 10, 2018.

[8][9] On February 5, 2018, Sinclair was cast as Rosalind "Roz" Walker in the Netflix series based on Chilling Adventures of Sabrina.