Van Gordon Sauter, a former television news executive, is married to the governor's sister, Kathleen Brown, who once ran for governor herself.
Sauter has experience with the commission, which regulates boxing and other fighting sports, having served as chairman a decade ago.
The position requires Senate confirmation and receives a $100-per-diem compensation.
The governor's office did not mention Brown's relationship to Sauter when it issued a press release on Wednesday that included his appointment.
Evan Westrup, a spokesman for Brown, said "pertinent information" is included in notices about appointments.
"Information on an appointee's spouse -- or other relatives -- is not," he said.
Sauter previously served as president of CBS News and Fox News, and worked as a journalist in the U.S. and internationally. He is not registered with a political party.