He is best known for the movies My Little Bride (2004), Sunflower (2006), The Prison (2017), as well as television series Love Story in Harvard (2004), Gourmet (2008), A Thousand Days' Promise (2011), Punch (2014–2015), The Doctors (2016), Black Knight: The Man Who Guards Me (2018), and The First Responders (2022–2023).

Kim Rae-won initially wanted to become a professional basketball player, but when an injured ankle tendon ended that childhood dream, he turned to acting and studied Theater and Film at Chung-Ang University.

[16][17] In 2008, Kim played an elementary school teacher who falls for a Korean-Japanese jewelry designer (Mirai Yamamoto) in the Japanese film Flower Shadow (花影, Hanakage).

[21][22] Kim impressed the audience with his portrayal of a character torn between the longtime girlfriend whom his parents approve of, and the woman he truly loves (Soo Ae) who suffers from early-onset Alzheimer's disease.

[23] In the 2012 film My Little Hero (released internationally as A Wonderful Moment), Kim played a cynical music director who "discovers" a young boy in an audition contest.

[45] On 28 September 2011, Kim was reportedly involved in a physical altercation with a waitress at a bar in Gangnam, Seoul where he and employees of his then-agency Bless Entertainment were drinking.

[47] Kim has long been rumored to come from a very affluent family, which he denied in a 14 January 2013 guest appearance on talk show Healing Camp, though he confirmed that he did inherit an apartment unit during middle school as well as a large sum of money from his grandmother.