She is the younger daughter of filmmaker Judd Apatow and actress Leslie Mann.

[3] Her father's family is Jewish, whereas her maternal great-grandmother was of Finnish ancestry.

[4] Her sister is actress Maude Apatow, with whom she worked on This is 40, Funny People, and Knocked Up.

[7][8] Her personal relationships with celebrities have received much media attention, particularly with "best friend" singer-songwriter Olivia Rodrigo,[9] as well as singer-songwriter Billie Eilish[10] and influencers Charli D'Amelio and Avani Gregg.

[11] Apatow began acting at age 5, when she appeared as Charlotte in the film Knocked Up, directed by her father.