Robert Joseph Jackson, 22, pleaded guilty to using an offensive weapon in company to prevent detention and causing grievous bodily harm to a person with intent to resist arrest and was sentenced in Sydney District Court on Tuesday.

Jackson was sentenced to eight years on both charges with a minimum of six years non-parole, dating back to his arrest in 2012.

Jackson was in a car with four other people which was being chased along the New England Highway near Glen Innes by police on November 1, 2012.

Patrick Garret suffered critical injuries and had to undergo emergency brain surgery after one of the rocks thrown smashed through his windscreen and knocked him unconscious while driving home on the New England Highway.

His father, who was also in the car, managed to steer the car and bring it to a stop two kilometres down the road.

Mr Garret delivered an emotional victim impact statement during the sentencing hearing detailing the nature of his injuries.

For more on the story, see tomorrow's edition of The Leader.