Sink made her Broadway debut as part of the original cast of the "Annie" musical revival. While still starring in the play, she also appeared in the Emmy-winning TV series "The Americans" as 'Lana'.
In 2015, she co-starred with Helen Mirren in "The Audience" on Broadway. In 2017, Sink began playing 'Maxine Mayfield', a skateboarder from an abusive household, in the Netflix series "Stranger Things".
October 2019, Sink starred in the Netflix horror feature "Eli" as 'Haley', a teenage girl who is later revealed to be the title character's older paternal half-sister. In 2021, Sink played the main role of 'Ziggy Berman' in "The Fear Street Trilogy", appearing in the second and third installments of the series, "Fear Street Part Two: 1978" and "Fear Street Part Three: 1666".
Sink also played the lead 'Tess DeNunzio' in the upcoming drama "Dear Zoe'. February 2021, Sink joined the cast of "The Whale". In November 2021, she played the lead in Taylor Swift's short film "All Too Well: The Short Film".