From Sheboygan County, Wisconsin, LeMahieu received his bachelor"s degree from Dordt College in business administration and political science. He is the owner of The Lakeshore Weekly in Oostburg, Wisconsin. LeMahieu served on the Sheboygan County Board of Supervisors and was the chairman.
On November 4, 2014, LeMahieu was elected to the Wisconsin State Senate as a Republican.
He succeeded Joe Leibham who did not run for re-election.