Nam Sang-mi was working in a Lotteria restaurant near Hanyang University in the fall of 2001 when someone posted her personal photos on the internet. Her popularity as an ulzzang led to her discovery as an actress. She made her debut in the 2003 melodrama series Love Letter, and began her acting career by taking small roles in films, TV dramas, and commercials. Her first leading role came with Sweet Spy in 2005. This was followed by leading roles in comedy drama Bad Family (2006) and action romance drama Time Between Dog and Wolf (2007).