Milligan grew up in Warkworth, Ontario in the municipality of Trent Hills.

He taught History and English at Campbellford District High School from 1998 until his election to the legislature.

[1] In the 2011 provincial election he ran as the Progressive Conservative candidate in the riding of Northumberland—Quinte West.

[3] During his tenure in parliament, he served as critic for interprovincial trade and education issues.

[4] In September 2017, Milligan sought the Progressive Conservative nomination for the new riding of Northumberland—Peterborough South.