Kim Ah-joong made her acting debut with a supporting role in the 2004 KBS sageuk Emperor of the Sea. In 2005, she landed her first big screen acting gig in the romantic comedy When Romance Meets Destiny, which won her the Most Popular Actress trophy at the 42nd Baeksang Arts Awards. Her career breakthrough came soon after when she was cast as lead in the hit musical romantic comedy 200 Pound Beauty, which earned her numerous acting citations including Best Actress at the 44th Grand Bell Awards. She also recorded the songs Beautiful Girl, Star, and a cover of the Blondie song Maria for the movie’s official soundtrack. In 2009, she acted alongside Hwang Jung-min in the KBS2 series Accidental Couple, which scored her an Excellence Award at the KBS Drama Awards. In 2011, she was nominated for Best Actress at the 47th Baeksang Arts Awards for her role as forensic doctor in the SBS medical investigation drama Sign. In 2017, she starred in the high-rating tvN time-slip series Live Up to Your Name, opposite Kim Nam-gil.

Kim Ah-joong earned a master’s degree in journalism and mass communications from Korea University. In 2011, she was fined by South Korea’s National Tax Service for failing to properly declare her taxable income.