Will Thomas Barnard was changing a flat tyre on the side of the highway at Legana about 11.30pm on December 27 last year.

While he and others were fixing the tyre, police turned up.

That was when the 21-year-old admitted to officers he had been drinking before jumping behind the wheel of the car.

He was breath tested and blew 0.195 - nearly four times the legal limit for a fully license driver.

Appearing in the Launceston Magistrates Court on Wednesday, Barnard pleaded guilty to one count of being a driver holding a provisional license with alcohol in their body.

As a P-plater, he was not legally allowed to have any alcohol in his system.

Magistrate Simon Brown described it as a "dangerously high" reading.

"This is a bad example of drink-driving," he said.

"You had no business behind behind the wheel of the car, you were a danger to yourself, to anyone else in the car, and anybody on the road or near the road.

"I'm not going to send you to jail today, but if you were to repeat anything like this, this will come back to haunt you."

The court heard Barnard had prior traffic matters.

Lawyer Grant Tucker said his client admitted he needed to "pull his head in", pointing out Barnard was not found behind the wheel, but had openly told police he was the driver.

Barnard was convicted and disqualified from driving for 15 months, from the date of the offence.

In addition to the $1250 fine, he was ordered to pay costs of $88.04.