The chair of the House of Commons Home Affairs Committee Yvette Cooper has called on the Parole Board to publish its reasons for deciding to release serial sex attacker John Worboys.
Former black-cab driver Worboys is believed to have carried out more than 100 rapes and sexual assaults on women in London between 2002 and 2008.
Victims' groups and charities have condemned the decision to free him.
Labour MP Ms Cooper said the ruling must be scrutinised before his release.
Worboys was convicted in 2009 of 19 charges of drugging and sexually assaulting 12 women passengers and one charge of rape.
He was ordered to serve at least eight years in jail but the following year the Met Police said other women had come forward and that the suspected total number of his victims exceeded 100.
When he is released from prison later this month, aged 60, he will have spent a decade in custody, including a period on remand.
However, the Parole Board's ruling has sparked outrage.
Ms Cooper said: "Given the seriousness of this case, the Parole Board should publish their reasons immediately so both the decision and the process can be scrutinised before this man is released.
"We also need to know what information and support was given to all the victims before this decision was taken."
The charity Rape Crisis described Worboys' period of incarceration as "woefully short" for such a "dangerous and manipulative perpetrator".
Sarah Green, from the End Violence Against Women Coalition, said the decision "beggars belief" and "is likely to be the product of a justice system and a society that cannot, and perhaps will not, deal with rape".
Worboys, a former stripper from Rotherhithe, south-east London, targeted young women who had been drinking in the West End of London
After deceiving them with a ruse that he had won the lottery, he produced champagne and a carrier bag stuffed with cash, before inviting them to celebrate with him.
But the alcohol was laced with powerful sedatives, and once the drugs had taken hold he attacked the women in the back of his cab.
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At his sentencing, during which he was described as a "repetitive predatory sexual offender", Worboys was told he would not be released until parole officials were convinced he did not pose a threat to women.
After a hearing about his case in November, the Parole Board decided to approve his release with "stringent" licence conditions. The period on licence lasts for at least 10 years and he can be sent back to jail if he breaches the conditions.
Worboys will also have to report to probation staff every week and is barred from contacting any of his victims.
In a statement on Thursday the Parole Board said: "We can confirm that a three member panel of the Parole Board has directed the release of Mr John Worboys, following an oral hearing.
"The arrangements for Mr Worboys' release will be managed by the Ministry of Justice."
One of Worboys' victims told BBC News she was unaware that his parole hearing had been successful and he was due to be let out.
And Harriet Wistrich, a lawyer who represents two of Worboys' victims, said neither woman had received a letter to inform them that the convicted rapist would be released.
She said one of the women felt she should not have had to "receive the news and see his face everywhere while cooking tea for her children".
Mrs Wistrich criticised the original sentence as being too short, saying it was just "one month per sexual assault".
She said: "It feels like another smack in the face, after having spent years battling for justice to [hold] the police to account for failing to investigate, that they've also not had the courtesy to inform her".
In 2014 Mrs Wistrich's clients won their High Court bid to receive compensation from the Met Police over the way the case was handled.
At the time Mr Justice Green said "systemic" failures in the investigation meant Worboys was not stopped earlier.
In 2010 Worboys had an appeal against his conviction thrown out by the Court of Appeal, where Lord Justice Moses labelled his offences as "appalling".
Malcolm Fowler, a retired solicitor of 48 years, said Worboys "would be anything but a free man" on his release from prison.
"The judge said he was going to serve at least eight years, and he has served a little more than that.
"Worboys is not walking a free man from prison. He is going to be on a very conscious monitoring system, and rightly so."
The Metropolitan Police said it would not be commenting on Worboys' release.
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