Leah McKendrick was born and raised in San Francisco, California. While studying at Chapman University she wrote, produced, directed, and acted in a number of short films and stage plays and graduated in 2008 with a BFA in theatre performance.

In 2014, McKendrick wrote, produced and starred in the pop musical web series Destroy the Alpha Gammas. The series was critically acclaimed, and she was made a Webby Award honoree and received a Streamy Award nomination. In 2017, she wrote, produced and co-starred in her feature debut, M.F.A., which premiered at South By Southwest. In 2019, she was hired to write Paramount's Grease prequel, Summer Lovin', which was later cancelled. In 2020, she wrote, directed and starred in the short film Pamela & Ivy, a feminist origin story for the supervillain Poison Ivy. The film premiered on Collider. The film was a Webby Award honoree for best writing.

In 2022, McKendrick wrote, directed and starred in the feature film about a broke, single 34-year-old woman that decides to freeze her eggs following a breakup. The film was based on her own experience with egg-retrieval in 2021. The film premiered at South by Southwest in March 2023 and was released theatrically by Lionsgate in 2024. She was named one of IndieWire's "28 Rising Female Filmmakers to Watch" in 2023.