Arcanie Vincent Optetaia Matagi has given up his year-long fight against a manslaughter charge and pleaded guilty before the start of a scheduled hearing for an illegal street racing death.

Matagi, a 25-year-old printer, was doing 150km/h and racing with another car when he lost control along the Main North Road and crashed into a car coming the other way, injuring the driver and killing the woman passenger, Laureen Helen Reilly.

Her death prompted her son, ACT political candidate Aaron Keown, to mount a campaign for harsher sentences for street racers.

Mr Keown was at court to see the guilty plea entered by Matagi.

He was remanded on bail for sentencing in the High Court on October 1 on the charges of manslaughter and dangerous driving causing injury.

Justices of Peace Nick Atkins and Bruce Dawson called for an updated pre-sentence report and home detention report, and banned Matagi from driving while he awaits sentencing.

Defence counsel Allister Davis said it was hoped that a restorative justice meeting could be held before the sentencing. At least one of the parties was prepared to meet Matagi, he said.

The fatal crash happened on May 6 last year, but has been delayed for a year after Matagi was allowed to plead guilty on September 17 to a charge of dangerous driving causing death.

A manslaughter charge had been laid earlier and it was not withdrawn at that stage. The crown later decided it wanted to go ahead with it.

That has led to a series of hearings with much of the detail suppressed. Finally, a few months ago, an out-of-town judge visiting Christchurch ruled that the crown would be allowed to proceed.

That led to the setting of a three-day depositions hearing to start today but the hearing never got going. Matagi pleaded guilty just as the court convened.

Mr Keown said after the hearing that the case should never have taken a year to reach this stage.

It had been poorly handled by the police, he said.

Crown prosecutor Barnaby Hawes said Matagi was alone in his car about 9.45pm on the night of the crash.

Along Prestons Road he was overtaken by a Nissan Skyline with 18-year-old Brad Jordan Nicholls driving.

Matagi began to chase the other vehicle at speeds of 120km/h.

They continued to the Main North Road where Matagi lost control, crossed the centre line, and crashed into a vehicle coming the other way. Police estimated his car may have been travelling at 150km/h at the point of impact.

The driver of the other car was seriously injured and Mrs Reilly was killed. Matagi's car was torn in half in the crash.

Police said earlier that Nicholls' car ploughed into the back of Matagi's car during the pile-up.

In September Nicholls admitted the charge of dangerous driving. He was sentenced to 200 hours of community work and disqualified from driving for 15 months.