Steve Ewanchuk (ee-WAHN'-chuk) was scheduled for statutory release next month but the board has decided he still poses a risk to the public.
The 65-year-old is to remain in prison until his warrant expiry date in 2018.
Ewanchuk has a criminal record of sex assaults on young girls and teens that spans four decades.
He came to notoriety in 1999 in what was dubbed the "no means no" court battle that clarified Canada’s sex assault laws.
The Supreme Court convicted him of sexual assault for groping a 17-year-old during a job interview, even though she told him three times to stop.
Alberta's Court of Appeal had upheld Ewanchuk's acquittal. Appeal Justice John McClung remarked that the young woman "did not present herself in a bonnet and crinolines" and that Ewanchuk’s advances "were far less criminal than hormonal."
The Supreme Court said the judge's comments reinforced a stereotype that women invite sex assaults through their appearance. The high court changed the country's sex-assault law to put the onus on the initiator of sex to obtain consent.
Most recently, in 2007, Ewanchuk was sentenced to 11 years for sexually assaulting an eight-year-old girl.
The sentencing judge also declared him a long-term offender, which means he will be under strict supervision for 10 years once he is released by the parole board.
Note to readers: This is a corrected story. A previous version had National Parole Board.