Snook, who pleaded guilty in May to 46 charges including sexual assault and possessing, distributing and making child pornography, showed no emotion as he was led away in handcuffs.
His crimes, which began in January 2001 and went on until his arrest in January of this year, involved 17 boys, most of whom were from the Saint John area and between the ages of five and 15 at the time of the offences.
"It's important for the victims to know that it was not their fault," said provincial court Judge Alfred Brien, adding that many of Snook's victims declined counselling.
"Regretfully, not all of the victims have come to terms with their abuse."
At his sentencing hearing in August, Snook said he was ashamed of his actions and told the court that he was sexually abused as a boy in Newfoundland.
"If anyone should have known better, it was me," Snook, 41, said at the time.
"I became the very thing I hated most: a person who molested children."
Snook's sister Donna declined comment on the sentence Thursday but said she thinks there should be mandatory counselling for the victims.
"Some of them are going to be, in 10 or 15 years, right back here in court and we're going to be doing this all over again," she said outside court.
"They should have counselling because some of them are going to continue the behaviour."
Snook was given 15 months credit for time already served, meaning he has 16 years and nine months left on his sentence. He will be eligible for parole after serving one-third of that.
The Crown had argued for a 21-year prison sentence, saying Snook created a "permissive atmosphere" in his suburban home by luring boys with cash, allowing them to consume alcohol and marijuana, and having them carry out sex acts.
Outside court Thursday, Crown prosecutor Karen Lee Lamrock said she was satisfied with the judge's ruling.
"He's handed down an 18-year sentence, which is one of the longest sentences ever awarded in Canada, and I hope that this will begin the healing for the victims," Lamrock said.
Defence lawyer Dennis Boyle had argued for a 12-year prison term, saying Snook is willing to help the victims in any way he can and is eager to undergo rehabilitation. But he said Thursday the sentence was appropriate.
"He's looking forward to the treatments that he can have and those are not only with his pedophilia, but he has received no treatment whatsoever for his own abuse as a child," Boyle said outside court.
Grace Murphy, who worked with Snook on a lunch program for youths, said she was disappointed he wasn't given a stiffer penalty.
"He's done so much damage to the vulnerable children and there was a lot of them," Murphy said. "It's sad."
Brien also ordered Snook to provide a DNA sample and he will be placed on the sex offender registry for the rest of his life.
Snook was arrested by the RCMP after an investigation that began in 2011 involving the Saint John and Toronto police. After his arrest, police seized his computers and discovered more than 15,000 photos and videos of child pornography, court heard.
He was elected to city council in 2008 and was involved in community organizations including the Inner City Youth Ministry, which provides sports programs, mentoring and lunches at three schools.
A forfeiture hearing has been set for Nov. 15, at which point the court will consider what to do with property seized during the investigation, such as Snook's home and computers, including a laptop belonging to the City of Saint John.
Snook also faces two counts each of sexual assault and sexual interference involving a boy for alleged incidents in the mid-1990s in Newfoundland. Boyle said the courts in Newfoundland have agreed to transfer those charges to be heard in New Brunswick and his client will plead guilty to them.
He said the New Brunswick Crown Prosecutors Office must still agree to accept the transfer of the charges and set a court date.