Born in South Boston, Massachusetts, Regan attended Saint Sebastian's School in Needham, Massachusetts. He began his career playing for the Waterloo Black Hawks of the USHL for the 2003–04 season. That year the Black Hawks reached the Clark Cup finals and Regan was named the Clark Cup MVP. He was drafted by the Bruins in the ninth round (277 overall) of the 2003 NHL Entry Draft then attended the University of New Hampshire. 

UNH advanced to the NCAA tournament each of the four seasons that Regan played.[5] He received several awards his senior season and was a finalist for theHobey Baker Award.[6] He was a unanimous selection as the 2008 Hockey East Player of the Year and also won the Walter Brown Award for best American college hockey player in New England.[6] In addition he was the All-Hockey East First Team goaltender and won Hockey East Defensive Player of the Week seven times.[7] He also set the UNH record for single season save percentage and was the first UNH goaltender to win twenty games in two consecutive seasons.[7] He graduated from UNH with a dual major in Finance and Economics. His highGPA earned him a spot on the Hockey East’s All-Academic Team.[8]

After graduating, he spent the 2008–09 and 2009–10 played two seasons playing in theAmerican Hockey League and the ECHL. He was signed by the Providence Bruins in 2008, where he initially served as a backup toTuukka Rask. He was called up to the Boston Bruins in January 2009.