Lee Kwang-soo began his entertainment career as a model. In 2008, he landed his first acting role in the SBS series The Scale of Providence. That same year, he became part of the MBC sitcom Here He Comes, in which he was nominated for Best Newcomer at the MBC Entertainment Awards. In 2010, he joined the SBS variety show Running Man and stayed with the program for 11 years. His work in Running Man won him numerous recognitions, including a Top Excellence Award at the 2016 SBS Entertainment Awards. In 2014, he took home acting honors at the Korea Drama Awards and the SBS Drama Awards for his portrayal of a café waiter with Tourette syndrome in It’s Okay, It’s Love. In 2019, he acted alongside award-winning actor Shin Ha-kyun in the film Inseparable Bros, which earned him Best Supporting Actor trophies at the 56th Baeksang Arts Awards and the 40th Golden Cinema Film Festival.

Lee Kwang-soo completed his mandatory military service before his entertainment industry debut. In 2018, his agency confirmed his relationship with actress Lee Sun-bin, whom he met on the set of Running Man in 2016.