[5][6] On April 10, 2019, she independently released her debut album, Off Brand, later signing with Republic Records in 2022.

[8] Her parents were Broadway performers, her mother as an actress and her father as a music director, conductor and record producer, so she grew up acting, singing and dancing.

[11] Kosarin, like many child performers, attended Brighton Hall School in Burbank, California.

[22] In April 2019, it was announced that Kosarin would appear in the second season of the Hulu horror series Light as a Feather,[23] in which she portrayed the role of Nadia.

[31][32] In July 2019, Kosarin was set to embark on a headline tour across the United Kingdom to promote the release of Off Brand, but this was later cancelled due to "scheduling conflicts".