Cait Cortelyou began acting at the age of 8, when she joined a Shakespeare troupe run by a pair of psychologists in her hometown of Madison, Wisconsin. Her mother is from an Ashkenazi Jewish family, while her father has Scotch-Irish ancestry. She is a descendant of Jacques Cortelyou, who created the first map of New York City.

Given her modern sensibilities combined with vintage looks, Cait has appeared in numerous period pieces, including Steven Soderbergh's The Knick (2014) set in 1900, the Off-Broadway hit "Sleep No More" set in 1939, and the independent feature film Ask for Jane (2018) set in the late 1960's, which Cait also created and produced, and which opened in theaters across the country in May of 2019. She also appeared as Delilah in the special fashion week episode of Bull (2016).

Cait earned her Bachelors degree from Barnard College of Columbia University, where she studied acting with Juilliard professors and graduated with honors over a year early. Cait is also an alum of the National Theater Institute at the Tony Award-winning O'Neill Theater Center in Connecticut, and has studied with the Royal Shakespeare Company in Stratford. She trained under acclaimed acting coach Anthony Abeson for two years, with improv coach Micah Sherman for one year, and studied Yat Malmgren character analysis and movement psychology with UK-based instructor Giles Foreman.