Kim Sun-ho started his acting career as a stage actor. He landed his television debut in the 2017 KBS2 workplace comedy Chief Kim. This was immediately followed by a main role in the KBS2 series Strongest Deliveryman. His work in the said dramas earned him a Best New Actor nomination at the 2017 KBS Drama Awards. Later in 2017, he became part of the MBC series Two Cops, in which he bagged the Best New Actor trophy as well as an Excellence Award at the MBC Drama Awards. In 2018, he starred in the tvN sageuk 100 Days My Prince, which became one of the highest-rated Korean cable dramas of all time. In 2019, he was cast in his first leading role in the tvN investigative crime drama Catch the Ghost, opposite Moon Geun-young. In 2020, he reached a major breakthrough in his career with his appearance in the hit tvN series Start-Up. His performance in the drama earned him a Best Supporting Actor for TV nomination at the 57th Baeksang Arts Awards.

Kim Sun-ho completed his mandatory military service prior to his screen debut. In late 2021, he was caught in a forced abortion scandal with his former girlfriend, for which he apologized.