Stefan Sylvestre was given a life sentence in 2009 for throwing acid at the former model, who is preparing to appear in the TV show Strictly Come Dancing.
The 30-year-old, from Shepherd’s Bush, west London, was told he must serve a minimum of six years before being eligible for parole.
Piper, 34, suffered horrific injuries during the attack and was left permanantly scarred after her ex-boyfriend Daniel Lynch had arranged for Sylvestre to throw the corrosive liquid in March 2008.
A spokeswoman for the Parole Board said: “We can confirm that a panel of the Parole Board directed the release of Mr Stefan Sylvestre following an oral hearing.
“Parole Board decisions are solely focused on whether a prisoner would represent a significant risk to the public after release.
“The panel will have carefully looked at a whole range of evidence, including details of the original evidence and any evidence of behaviour change.
“We do that with great care and public safety is our number one priority.”
According to the Parole Board’s summary of the oral hearing, Piper had read statements in person to the panel.
It said: “The panel took full account of the content of these statements and the supporting documentation.”
But the summary went on to say that there was “a number of things” which “reduced Mr Sylvestre’s risk of causing serious harm in the future”.
“Mr Sylvestre is now 30 years of age and was just 19 when he committed the index offence,” it said. “He was drawn into a criminal lifestyle in his teens and was involved with drugs.
“During his time in custody, Mr Sylvestre has actively avoided anti-social behaviour within the prison and has avoided violence, despite being under threat.
“He has behaved well to distance himself from such influences. He has repaired his relationship with his family, has gained employment-related skills and improved his education.
“He has not been involved in drugs in prison and has completed relevant offence-focused work to challenge and change his attitude and thinking.”
A forensic psychologist told the panel Sylvestre’s improved relationship with his family and future plans were among factors which would prevent him from reoffending, according to the summary.
It added: “Mr Sylvestre displayed empathy for the victim and expressed remorse and shame for his actions.”
The Ministry of Justice (MoJ) said its “heartfelt sympathies” were with the TV presenter but added that it was “vital that we respect the independence of the Parole Board”, which it said carried out “full risk assessments” before making a decision.
However, a spokesman said the MoJ was carrying out a full review of Parole Board rules in a bid to “increase transparency and ensure victims are supported”.
Lynch was jailed for life with a minimum of 16 years for sexually assaulting Piper and telling Sylvestre to throw acid on her.
At the time of their court case, the two men were described by Judge Nicholas Browne QC as being “the face of pure evil”.