Russell John Tully has been found guilty of murdering two Ashburton Work and Income employees.
Tully, 49, has been on trial in the High Court in Christchurch for the past two weeks for the shooting which took place in the WINZ office on 1 September 2014.
He was also found guilty of attempting to murder case manager Kim Adams, but was found not guilty of attempting to murder Lindy Curtis, who was shot in the leg.
Tully represented himself in the trial but was assisted by friends of the court Phil Shammy and James Rapley.
Yesterday Justice Cameron Mander summed up the case and the jury retired at 4pm to consider a verdict.
They returned at 9.30am today and after more than seven hours of deliberations found Tully guilty of the murders of Peggy Noble and Leigh Cleveland.
Over the last two weeks the court has heard evidence from about 70 witnesses including the two women Tully was also accused of attempting to murder.
Last week Miss Curtis, who was shot in the leg as she hid under her desk, gave emotional testimony.
"I was sitting at my desk helping a client when I heard a blast ... When I looked up, I could see a man in a balaclava with a gun. I thought it must be a hoax or that he was going to take us hostage."
That thought only lasted seconds as the gunman started moving around the office, she said.
"I told my client to get under the desk and I joined him. I don't remember the exact sequence of events but I remember watching his feet moving around the office."
The next thing she knew, the gunman was in front of her.
"I could see him holding the gun; the last thought that went through my mind was that I was history, and I wondered who would take care of my family."
The Crown said Ms Curtis avoided being killed only by raising her leg when the shots were fired, which shielded her body.
"I remember him looking at my leg. He could tell he had shot me in the leg, so I thought he would finish me off and shoot again, but he didn't," Ms Curtis said.
She recalled hearing another woman pleading for her life. "I could hear a very emotional voice saying: 'Please, I beg you, I beg you, you don't have to do this', then I heard a blast."
Ms Curtis told the court she did not recognise the voice because of the emotion in it.
During his opening address Crown lawyer Andrew McRae told the jury Mr Tully was intent on killing as many staff members as possible, but was also bent on targeting Ms Cleveland and Ms Adams - against whom he had a grievance.
Mr McRae told the court when Tully was arrested, he had a piece of paper with the words, 'Leigh Cleveland', 'Kim Adams' and 'discrimination' on it, which he said showed Tully's intent.
David Cooze who chased the masked gunman down the street after the shooting also gave evidence.
Mr Cooze said he was talking to receptionist Ms Noble when the masked gunman walked into the office and shot her.
Covered in gunpowder, Mr Cooze ran from the building.
Once the shooter left the building, he confronted him, ignoring warnings that he would be shot if he did not back off.
"He started freaking out. I rattled him that much he dropped his helmet and bike lock on the ground."
Mr Cooze ran after the gunman, coming within a metre of him as he made off on his push bike, but could not catch him.