At the end of the 2010 season, Kirby left Gloucestershire for West Country rivals Somerset signing a three-year contract with the County Championship Division One side. Before linking up with his new county Kirby was involved in the MCC squad for the Champion County match taking 5 for 29, before his match was ended with a foot injury. He played in the fixture on four occasions. Kirby's first season with Somerset saw him take 53 wickets at an average of 31.54 as Somerset finished 4th in Division One of the County Championship. He also appeared in two domestic finals and was part of the Somerset side that reached the semi-finals of the 2011 Champions League Twenty20 in India.