Kang Shin-il debuted as a theater actor in the 1985 stage production of Chilsu and Mansu. In 1988, he landed a role in its film adaptation, which was directed by Park Kwang-su. In 1999, he was named Best Actor at the 35th Dong-A Theater Awards for his performance in Kimchigook Goes Crazy. In 2002, he was cast in the action film Public Enemy, which won him Best Supporting Actor at the 10th Chunsa Film Art Awards. In 2005, he was nominated for Best Supporting Actor at the 42nd Grand Bell Awards for Another Public Enemy, which is the sequel to the 2002 film. That same year, he became part of the KBS2 series Resurrection, which gave him another Best Supporting Actor nomination at the KBS Drama Awards. In 2007, he starred in the horror film Black House, which earned him a nomination for Best Supporting Actor at the 45th Grand Bell Awards. He later returned for the third installment of the Public Enemy film franchise titled Public Enemy Returns, which scored him yet another Best Supporting Actor nomination at the 7th Korean Film Awards. As for his recent works, he played memorable characters in the widely popular KBS2 series Descended From the Sun in 2016 and also in the tvN period drama Mr. Sunshine in 2018.

Kang Shin-il studied electronic engineering at Kyung Hee University. In 2007, he was diagnosed with liver cancer, which forced him to go on hiatus. He returned to acting after a successful surgery.