After modeling for teen magazines, Im made her acting breakthrough in Kim Jee-woon's horror film A Tale of Two Sisters (2003), followed by the popular television series I'm Sorry, I Love You (2004).

She then moved onto acting and debuted in the teen drama School 4,[3] but it was Kim Jee-woon's 2003 stylish horror A Tale of Two Sisters that first drew her critical notice and newcomer awards.

[6][7] With Im looking much younger than her age, those projects solidified her image as an eternal ingenue, as did touching character study ...ing,[8] horse jockey film Lump Sugar,[9] and Park Chan-wook's surrealist I'm a Cyborg, But That's OK.[10] In 2007, she began shedding that image by taking on more adult roles,[11] notable among them Hur Jin-ho's romantic melodrama Happiness,[12][13] Choi Dong-hoon's blockbuster fantasy Jeon Woo-chi: The Taoist Wizard,[14][15] romantic comedy Finding Mr. Destiny[16] and Lee Yoon-ki's minimalist breakup indie Come Rain, Come Shine.

[21][22] Im and Lee Jung-jae played two artists in a post-apocalyptic environment in the short film El Fin del Mundo ("The End of the World"), which screened at the prestigious contemporary art exhibition dOCUMENTA.

[27][28] In 2015, Im starred in Perfect Proposal, a remake of British crime thriller Woman of Straw that was partly shot in Macau.