Lee Sung-kyung started out as a model in 2008 before transitioning into acting in 2014 through the SBS series It’s Okay, It’s Love. The following year, she appeared in the MBC weekend drama Queen’s Flower, which won her Best New Actress at the MBC Drama Awards. In 2016, she joined the main cast of the tvN romance drama Cheese in the Trap and the SBS medical series Doctors. That same year, she played the titular character in the MBC coming-of-age sports drama Weightlifting Fairy Kim Bok-ju, which earned her an Excellence Award at the MBC Drama Awards. In 2019, she acted alongside Ra Mi-ran in the crime comedy film Miss & Mrs. Cops, which gave her the Special Popularity Award at the 24th Chunsa Film Art Awards. In 2020, she starred in the hit SBS series Romantic Doctor Teacher Kim 2, which scored her acting trophies at that year’s Asia Artist Awards and SBS Drama Awards.

Aside from modeling and acting, Lee Sung-kyung also ventured into singing. In 2016, she recorded a cover of Sharp’s My Lips Like Warm Coffee together with Eddy Kim. In 2017, she was featured in Psy’s song Last Scene from his album 4×2=8.

Lee Sung-kyung graduated from Dongduk Women’s University in 2016. She was previously in a relationship with her Weightlifting Fairy Kim Bok-ju co-star Nam Joo-hyuk.