Merriman's first major role was on the television series "The Mommies", which ran from 1993 to 1995. During the 1990s, he appeared in most episodes of "The Pretender" as a younger version of the title character. He has starred in several television films, including "Smart House", "The Luck of the Irish", and as a young Meyer Lansky in "Lansky". He appeared in the 1999 feature film "The Deep End of the Ocean", playing the lost son of Michelle Pfeiffer's character, and subsequently starred as the main character, a Jewish boy from the Bronx, in the 2000 film "Just Looking". In 2002, he played Adam Eddington in another Disney Channel original movie, "A Ring of Endless Light". He then returned to television roles, appearing in "Dangerous Child", "Taken", and "Smallville".