Prior to his current position, Merila attended University of Minnesota and was drafted by Major League Baseball teams twice - first, he was taken in the 10th round of the 1993 draft, though he refused to sign. He was next taken by the Padres in the 33rd round of the 1994 draft, beginning his professional career that year. While with the University of Minnesota, he played on the school's baseball team, and was named Big Ten Conference Baseball Player of the Year in 1994.
He played for the Spokane Indians in 1994, hitting .253 in 54 games. In 1995, he played for the Idaho Falls Braves, hitting .284 in 56 games. Overall, he hit .268 in his two-year career. He also pitched in two games, posting a 32.40 ERA.
He retired from professional baseball due to a brain tumor. Following his playing career, he became the Padres' bullpen catcher. After the tumor returned in 2005, he was forced to give up his bullpen catching duties, however he still served as an aide to third base coach Glenn Hoffman.
After recovering from his second bout of brain cancer, he returned to the job of bullpen catcher, then in 2012 was made a team scout.