The judge said he had used methamphetamine and cannabis the night of the incident.
There was also a warrant out for his arrest, for breaching bail conditions.
Just three days before the anniversary of the woman's death, her mother read a victim impact statement in court.
She spoke of her utter devastation for her, her family and friends at the loss of her only child, as Lawson listened from the dock.
Lawson pleaded guilty to the charge of reckless driving causing death. He has a number of previous convictions, which include two for driving dangerously, five for reckless driving, one for careless driving, seven for failing to stop for police and a number of convictions for driving while disqualified.
In a letter to the court, Lawson said he had a volatile relationship with the victim who had a history of mental illness.
Lawson said he was concerned for the 21 year old's mental health and was driving her to the hospital, but could not find it.
Justice Thomas said if that was the case, Lawson should have stopped for police when they began following him and asked for help.
On the night of the incident, Lawson and the victim were parked up in his car, when a passing police officer approached them. Lawson drove away, travelling 10kmh above the 70kmh speed limit in the area.
He sped through two roundabouts, cutting across both lanes, at which point police sounded their sirens to signal him to stop.
Lawson continued driving before losing control at Mungavin interchange, sliding across the road into a median barrier.
However he kept driving, the wrong way around the interchange and over the Mungavin overbridge on the wrong side of the road. He overtook a bus and narrowly missing a head-on collision.
Travelling at about 107kmh and with the police close behind him, Lawson overtook another vehicle on a blind corner and had to swerve to miss an oncoming car.
Lawson's car then fishtailed several times before it slid across both lanes and crashed through a fence into a large pohutakawa tree.
The passenger's side of the vehicle caved in, compacting the victim's seat to about one-third its original width. She died from her injuries.
Lawson admitted smoking methamphetamine about an hour before the crash.
He received severe injuries including a broken neck, fractured back, several facial fractures and skull fractures.