[5] He debuted as a runway model in 2009 at the age of 20 and began appearing in prêt-à-porter and Seoul Fashion Week collections.

Kim fell in love with acting, saying, "I found myself feeling the same thrill and enthusiasm that I felt the first time I came to walk on the runway".

[8] Under the stage name Kim Woo-bin, he made his acting debut in 2011, starring in the mystery drama White Christmas and the low-rated cable sitcom Vampire Idol.

[4][9][10] In 2012, he had a supporting role in the romantic comedy drama A Gentleman's Dignity, written by famed screenwriter Kim Eun-sook.

The same year, he was cast in Kim Eun-sook's teen drama The Heirs,[15] which became popular domestically and internationally with a peak audience rating of 28.6% and 1 million hits on the Chinese streaming website iQiyi.

[20] Kim then appeared in his first major film role in Friend: The Great Legacy, the blockbuster sequel to Kwak Kyung-taek's 2001 box office hit.

In January 2014, he was cast in the heist movie The Con Artists, in which he played a top safe-cracker alongside rising star Lee Hyun-woo.

[25][26] Kim then appeared in an ad campaign for Calvin Klein Watches + Jewelry, making him the first East Asian model for the brand.

[27] In 2015, Kim was cast in his first television leading role in the melodrama Uncontrollably Fond, written by screenwriter Lee Kyung-hee.

[46] On March 8, 2022, Kim donated ₩100 million to the Hope Bridge Disaster Relief Association to help the victims of the massive wildfires that started in Uljin, Gyeongbuk.