Martin McDermott was found guilty of the manslaughter of Garda Gary McLoughlin in Co Donegal in December 2009.
McDermott, 25, of Castlegrove, Raphoe, was also found guilty of the reckless endangerment of Garda Bernard McLaughlin.
He had previously pleaded guilty to dangerous driving causing death, drink-driving, driving without insurance and driving while disqualified.
The jury was later told that McDermott has been in custody for the past year and a half.
The jury of eight women and four men took just under two hours to return their verdict.
McDermott showed no emotion as both guilty verdicts were read out by the jury foreman.
His mother and other relatives broke down in tears.
Some of the late Garda McLoughlin’s relatives, who travelled from their hometown of Fenagh in Co Leitrim, also broke down in tears.
The dead Garda’s brother Enda told the court that his family’s lives will be changed forever because of Gary’s death.
“Gary is in our thoughts every hour of every day. We got a phonecall nobody wants to hear at 3am. Our hearts would be broken and our lives changed forever,” he said.
He revealed how his father Noel is angry when people describe Gary’s death as an accident and is still have problems accepting his youngest son’s death.
Fighting back tears at Letterkenny Circuit Court, Enda also revealed the family thought he might pull through even though he was only given a 5% chance.
“When that increased to 15% we felt elated but we were soon punched in the stomach,” he said.
He described his brother as an ordinary, happy young man who loved his job and loved to do magic tricks for his nieces such as pulling coins out of their ears.
“It is difficult but we just miss those normal days,” he said.
He added that his mother Una finds it difficult to sleep and she says there is an emptiness in her life that she will never be able to fill.
The trial, which lasted three days, heard how Garda detectives first spotted McDermott speeding out of The Grove petrol station in Bridgend after 1.20am on December 13th, 2009.
The followed him and a chase ensued for more than 30kms with McDermott reaching speeds of up to 180kph.
The pursuit ended when McDermott, 25, smashed head-on into a marked patrol car at Lisfannon, Burt.
Garda Gary McLoughlin, 24, the driver of the patrol car, died the next day as a result of his injuries in hospital.
Prosecuting barrister Alex Owens SC said in summing up there was enough evidence to reach a verdict of involuntary manslaughter.
He said McDermott’s average speed during the pursuit across Donegal was 150 kph or 93mph.
“That speaks for itself what was going on. He was driving after he had been drinking and while he was disqualified from driving.
“This was a decision taken by the accused,” he said.
He also added that it was only by chance that McDermott did not come across any members of the public while travelling at such high speeds.
However defence barrister Peter Finlay SC said there was simply not enough evidence to find a verdict of manslaughter against McDermott.
He said Garda evidence stated that the minimum speed during the crash was between 51 and 59 kph – within the speed limit.
He also said the jury should not be influenced by the fact that the victim was a member of An Garda Siochana.
“Just because the injured person was a guard cannot influence your decision and that is said without the slightest disrespect to the force.
“I am not turning this into some Garda bashing exercise but it’s my duty to point out the facts. If that was the head of a Government or a labourer with a shovel on his back, it does not matter a wit in the eyes of the law.
“You cannot say I want to help the Gardai here if you are to truthfully follow the Oath,” he said.
In summing up Judge John O’Hagan said the fact that Gary McLoughlin was a Garda should not influence their verdict.
“You must look at the case in the cold light of day. You are not deciding this case to keep anyone happy.
“You are here to apply the law and bring in a true verdict according to the evidence,” he said.
After McDermott was found guilty of both charges, Judge John O’Hagan passed sentence.
He was told that the accused had 91 previous convictions – many of which were for traffic offences including drink driving as well as burglary and forgery.
He jailed McDermott to 8 years in prison for the manslaughter charge and suspended the last year.
He sentenced him to a further 5 years for the reckless endangerment to Garda Bernard McLaughlin.
On the dangerous driving causing death charge which McDermott pleaded guilty to, he was sentenced to 5 years and disqualified form driving for 20 years.
He received a further six months for drink driving, another 6 months for having no insurance and a further six months I jail for driving while disqualified.
All sentences are to run concurrently.
Judge John O’Hagan said he wanted to send out a message to all young drivers about their consequences of their actions.