Pier Giacomo Grampa, 77, exceeded the limit by 40 kilometres an hour while driving on the A12 motorway between Fribourg and Bern last autumn, he admitted in an interview aired by RSI on Tuesday night.
In November, Grampa stepped down as bishop for the diocese in the southern canton of Ticino after 10 years in the job.
He said the incident occurred in September as he was driving home from a conference of Swiss bishops at Givisiez in the canton of Fribourg.
“I did not notice that I was driving much faster than was allowed,” he said.
“The flash of the radar brought me back to reality.”
The matter was kept a secret while Grampa was officially still bishop.
He paid a fine and gave up his licence for three months.
That left him having to walk and use public transport for the month of December, RSI said.
He was bought a new car, which has been modified to limit the top speed, the broadcaster said.