Lee Da-in debuted as an actress in 2014 with a lead role in the tvN miniseries Twenty Years Old. That same year, she had a cameo appearance in the film The Fatal Encounter. In 2015, she became part of the MBC drama Make a Woman Cry. She then joined the KBS2 sageuk Hwarang in 2016 and the hit KBS2 weekend family drama My Golden Life in 2017. In 2018, she played a police detective in the MBC series Come Here and Hug Me. In 2019, she was cast in the KBS2 medical drama Doctor Prisoner. In 2020, she acted alongside Kim Hee-sun and Joo-won in the SBS sci-fi romance series Alice, which earned her a Best New Actress nomination at the SBS Drama Awards.

Lee Da-in studied theater and film at Hanyang University. Her parents are actors Kyeon Mi-ri and Im Young-kyu. Her older sister Lee Yubi is also an actress. She is dating actor Lee Seung-gi.