Go Soo first appeared in a soft drink TV commercial in which he waits for his girlfriend at curfew, followed by a role as an extra in the 1998 music video “Last Promise” by the band Position. He made his television debut in 1999 through the MBC sitcoms My Funky Family and Jump. Go drew critical praise for his performance in the television drama Piano in 2001, with one review describing him as an “actor with precision.” Piano was his first TV series produced by SBS; he signed an exclusivity contract with the broadcast network, and thereafter all of his dramas have been SBS-produced.

Go made his big screen debut as a drug crime officer in 2004’s Some, in which he performed his own stunts and was later recognized as Best New Actor at the Grand Bell Awards. In 2005, he starred in the revenge drama Green Rose, which was shot on location in China and Korea. He played a simple man who falls in love with a rich woman and gets accused of a crime he did not commit. Then in the romantic comedy Marrying a Millionaire, Go played a delivery man who is asked by a TV producer to act like a rich bachelor to attract several women on a televised reality dating show.