The man who broke Green Party co-leader James Shaw's eye socket in a random attack in Wellington has been sent to prison.

Paul Raymond Harris, 47, approached Shaw as the politician was walking to Parliament from his home in Karori, and attacked him.

Harris appeared in the Wellington District Court today for sentencing, after earlier pleading guilty to one count of injuring Shaw with intent to injure. He told the court in an earlier hearing he was driving to work when he saw Shaw walking down the street on March 14, so made a U-turn and parked his van.

He said he initially wanted to talk to him and had been "overcome with grief with the recent loss of a child" when his wife miscarried a couple of days before.

He said "all the talk on the airwaves about abortion" meant his emotions were running high.

Judge Ian Mills said in court today that Harris recognised Shaw as someone "who you had seen on TV and someone who has promoting a relaxation of the abortion laws, something which you disagree with".

"What happened next is what puts you in the dock today."

Shaw turned to leave, and Harris then grabbed him by the lapel and punched him in the eye, continuing to hit him three or four times before pushing him to the ground.

Paul Raymond Harris in the dock at Wellington District Court for sentencing on assaulting Green Party co-leader James Shaw. Photo / Melissa Nightingale

A witness was walking to work with her husband when they intervened and stopped the assault, after she saw Shaw curled on the ground and Harris standing over and punching him.

In court, defence lawyer Marty Robinson said Harris was remorseful, and that he had a "very limited" history of criminal offending.

He said it would be "unfortunate and unusual" for Harris to go to prison for "punching" but appreciated Harris had put himself in that position by saying he did not want an electronically-monitored sentence.

He said Harris was a "strong believer that abortion is the killing of humans" and that, along with the recent miscarriage, were "going through his head" when he made the poor decision to jump out of his car and start talking to a politician on the street about it.

Judge Mills said Harris had previous drink-driving convictions from the 90s and a disorderly behaviour conviction from 2004, "but in the circumstances all have little relevance, if any, to the sentencing today".

Harris was entitled to his views, but "you're not entitled to use violence to express those views".

He has been trespassed from Parliament grounds due to his behaviour over the past year, but Judge Mills did not explain what that behaviour had been.

According to Shaw's victim impact statement, during the attack "he just simply didn't know when the hitting would stop".

He has been less inclined to go out since the assault, and it has impacted on his family and staff.

After being treated by paramedics at the scene of the attack, Shaw continued on to work, but had to visit the hospital emergency department after his nose started bleeding later in the day.

It was discovered his right orbital plate was fractured, and the injury had been bleeding into his sinuses.

In his statement, Shaw said Harris did not actually refer to abortion or the miscarriage during the attack, instead talking only about the United Nations and beneficiaries.

During an interview with a probation officer before the sentencing, Harris called the officer part of the system and accused him of being "evil", Judge Mills said.

Psychiatric reports have not identified any mental illnesses or psychosis.

During sentencing, Harris asked the judge about the rights of the "50 citizens that have lost their life today".

"Fifty babies approximately lost their life today ... those are the citizens that I am speaking on behalf of," he said.

Judge Mills sentenced Harris to nine months in prison, but gave him leave to apply for an electronically monitored sentence.