In August 2008, Lee was awarded his master's degree from Dongguk University's Department of Theater & Film Art in the Graduate School of Cultural Arts. He made his first foray into theater in December of that same year, taking on the titular role in Hamlet in Water. The play ran for four days at his alma mater's Lee Hae-rang Theater.
Apart from his acting, Lee is known for launching a chain of upscale Italian restaurants in Seoul named after his movie Il Mare. Having studied interior design, he himself took responsibility for designing the interiors of his restaurants. Lee also founded the real estate development company Seorim C&D in 2008, and owns several businesses with actor Jung Woo-sung, his best friend since they starred together in City of the Rising Sun. In May 2016, Lee and Jung established and became CEOs of their entertainment label called the 'Artist Company'.