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. He is married with two young daughters and operates a small beef farm.
In the 2011 provincial election he ran as the Progressive Conservative candidate in the riding of Northumberland—Quinte West. He defeated Liberal incumbent Lou Rinaldi by 707 votes. In the 2014 election he was in rematch with Rinaldi but this time lost to him by 3,887 votes.
In September 2017, Milligan sought the Progressive Conservative nomination for the new riding of Northumberland—Peterborough South. Milligan lost the nomination to David Piccini on September 23, 2017.
