The 27-year was jailed for 30 months last November on charges of accepting corrupt payments during the Lord's Test against England in August 2010.
Butt, team mates Mohammad Asif and Mohammad Amir, and agent Mazhar Majeed were accused of contriving deliberate no-balls in return for money.
Amir was released in February after serving half his six-month sentence while Asif, jailed for 12 months, was freed in May.
Butt's father Zulfiqar said his son was being released early.
"We expect him to be released tonight," he told private channel Geo.
"My son's good behaviour has led to the decision and he will be in Pakistan in the next three to four days," Zulfiqar added.
Butt's wife and elder son visited him in jail last month.
The three players were banned for at least five years by the International Cricket Council (ICC), which has ordered the Pakistan Cricket Board to rehabilitate the former stars.
Amir started rehab last week.
The trio has a right to appeal the ICC ban in the Court of Arbitration for Sports in Switzerland.
Amir, who pleaded guilty during the trial, has decided not to appeal but Asif and Butt have hinted that they will challenge the punishment.
COMMENTS (4)
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Return of the Traitor !
The first four starting words sums it all!
Why couldn't he show good behavior before? Is he going to continue to deny the truth or show remorse, oh, who I am kidding. He is as innocent as morning dew; if you don't believe me ask him and his family who are responsible too.