Kent Sorenson pleaded guilty to obstruction of justice and causing a campaign to falsely report expenditures.
The charges stem from when Sorenson switched loyalties from U.S. Rep. Michele Bachmann, whose state campaign he headed in Iowa, to then-U.S. Rep. Ron Paul. The U.S. Department of Justice says he then lied to federal investigators about the money.
In the plea agreement, Sorenson admitted receiving and lying about monthly payments of roughly $8,000 from October to December 2011, when he was still named Bachmann's state chairman.
Sorenson could face up to 20 years in prison for obstruction of justice, and as many as five years on the second charge.
Sorenson, 42, resigned from the Iowa Senate last year.