Bruno Dey was found guilty as an accessory to the murder of 5,232 prisoners between August 1944 and April 1945. Five thousand deaths were attributed to those who died after they were denied food, water and medication during a typhus outbreak.
Two hundred were gassed with Zyklon B, and 30 deaths were caused by a device that killed via a shot to the neck.
Dey had not personally fired a gun to cause any of the deaths. Earlier in the trial, he said he was not guilty because he "didn't do direct harm to anyone."
"The concentration camp Stutthof and the mass murder that took place inside was only able to take place with your help," Judge Anne Meier-Göring told him in her verdict.
"For you it [Stutthof] was not hell, it was monotonous work."
Because he started working at Stutthof when he was 17, Dey faced a juvenile court for his charges, CNN said.
Since October, more than 40 co-plaintiffs have testified against him.
Ben Cohen, the grandson of one of the co-plaintiffs, said the verdict had "symbolic justice" for his grandmother, who was imprisoned at Stutthof.
"This verdict sends a powerful message that a guard in any camp cannot deny responsibility for what happened," he wrote in a statement.
Dey insisted he had been forced into his role. He was tasked with manning a tower, standing watch next to a gas chamber, according to the BBC.
He stated he was not aware of the "extent of the atrocities" that occurred at Stutthof, where it is believed 65,000 died. His prosecutors argued that he was relatively unimportant and had not directly contributed to the death toll.
However, he had admitted knowledge of the gas chambers and recalled seeing "emaciated figures."
"If only you had wrestled with your conscience," said the judge, according to The Guardian.
On the penultimate day of the trial, Dey apologized to those who had suffered.
"Today I want to apologize to those who went through this hellish madness and their relatives. Something like this must never be repeated," he said.
He was given a two-year suspended sentence.
The legal proceedings continued despite the coronavirus pandemic.
Court sessions were limited to twice a week for two hours each, with Dey inside a Plexiglas box. The majority of plaintiffs gave testimonies via video calls.
It is thought to be one of the last criminal cases for an individual involved in the Holocaust. Another guard from Stutthof is set for trial in Wuppertal, pending a medical assessment to determine his fitness to appear in court.