The Republican won re-election last year despite revelations he had affairs with patients and once urged one of them to seek an abortion.
He was fined $500 for two counts of unprofessional conduct, and is responsible for up to $1,000 in costs for the panel's investigation. He did not contest the findings
The ruling comes in response to two complaints filed by Citizens for Responsibility and Ethics in Washington, which called the penalties "piteous."
"This decision demonstrates that Tennessee's ban on sexual exploitation of patients is essentially meaningless," Melanie Sloan, the group's executive director, said in a statement. "Doctors in the Volunteer State can freely prey on patients with little fear of repercussions."
The watchdog group has also filed an ethics complaint in the U.S. House.
DesJarlais did not immediately return a message seeking comment from The Associated Press. But the congressman told The Tennessean newspaper: "I take responsibility for past mistakes and am happy to get this resolved."
DesJarlais nevertheless called the complaint politically motivated, saying it's "somewhat ironic" that he had gone without any complaints filed against him in the 20 years he practiced before his election to Congress.
DesJarlais has already drawn two Republican challengers in advance of next year's primary. State Sen. Jim Tracy and state Rep. Joe Carr have far outraised the incumbent through the first quarter of the year.
During his 2010 and 2012 campaigns, DesJarlais tried to cast doubt on reports of violent behavior and multiple affairs before his divorce was finalized in 2001. But court transcripts released the week after the election showed he admitted to eight affairs, encouraged a lover to get an abortion, which he publicly opposes, and used a gun to intimidate his ex-wife during an argument.
The sworn testimony also revealed for the first time that the congressman had agreed when his ex-wife had two abortions.