Merrill began his senior career with the Coquitlam Adanacs of the Western Lacrosse Association, and later the Brampton Excelsiors of Major Series Lacrosse, winning two consecutive Mann Cup championships (2008–2009).
Merrill's senior lacrosse career was marked by his time with the Coquitlam Adanacs and the Brampton Excelsiors, where he won two consecutive Mann Cup titles.