Barrett received a Bachelor of Arts degree from the University of Guelph in 1968, and a Master of Science degree from the Ontario Agricultural College in 1974. He later worked as a teacher of High School agriculture, and has been a partner in Farmleigh Farms since 1980. He is also a past president of the Norfolk Farm Safety Association, and a member of the Norfolk Federation of Agriculture.
In 1999 and 2003, he was re-elected in Haldimand—Norfolk—Brant. On the latter occasion, he defeated Liberal Rob Esselment by about 3,000 votes.
Barrett supported Jim Flaherty's unsuccessful bid to succeed Ernie Eves as leader of the Progressive Conservative Party in 2004.
In the 2007 Ontario general election, Barrett was easily re-elected, defeating Liberal candidate Lorraine Bergstrand by 26,100 votes to 9,500 votes in the newly redrawn riding of Haldimand-Norfolk.