Greig, 61, who was also ordered to pay $150,000, pleaded guilty in March to charges of conspiracy to harbor a fugitive, identity fraud and conspiracy to commit identity fraud, and identity fraud, the Associated Press reported.
Prosecutors had sought 10 years in prison while Greig had been facing a maximum 15 years.
In sentencing her, US District Judge Douglas Woodlock said: "We are all responsible for what we do. We all make choices. There is a price to be paid."
Bulger, the former leader of the notorious Winter Hill Gang who has also been accused of mass murder, is awaiting trial on charges he participated in 19 murders.
The 82-year-old, who was captured with Greig last year in Santa Monica, California, pleaded not guilty to the charges, the Washington Post reported in March. His trial is scheduled to begin November 5.
In pleading guilty last March to her charges — and thus avoiding a trial — Greig admitted to posing as Bulger’s wife and using a number of aliases and false identification to see doctors, buy prescription drugs and pay rent on their apartment.
According to the AP, her lawyer, Kevin Reddington, appealed for leniency, saying his client fell in love with a "Robin Hood" like figure.
She had simply never believed that her boyfriend — one of the FBI's Ten Most Wanted fugitives — was a murderer, Reddington told the judge.
Greig, who showed no emotion during the sentencing, reportedly nodded to her twin sister in the front row as she was led from the courtroom.
Steve Rakes, who says his South Boston liquor store was taken over by Bulger, told NECN the eight-year sentence was too lenient.
“Stone faced. She reminds me just of Bulger. Bullet piercing eyes. She has no heart,” Rakes said of Bulger's demeanor in court. “She probably sleeps in an ice chest.”
NECN also interviewed legal analyst Randy Chapman who called it "one of the tougher sentences I've ever seen on a fugitive from justice case."
However, Rakes called eight years "a cake walk."
“Whitey Bulger couldn’t have been on the run this long without her. She was his everything. And it’s pretty sad,” Rakes said. “Without her, there was no him. He couldn’t tie his shoes.”