The 57-year-old brutally bludgeoned his wife Celine Cawley to death in their plush home in the Dublin suburb of Howth in 2008.
He was sentenced to seven years in prison in February 2010 after being found guilty of the manslaughter of his wife. He was cleared of the charge of murder.
In December 2008, Gardai arrived at the family home on Windgate Road and found Lillis standing over his wife's body.
He claimed that she was killed by an intruder but his amateurish tale unravelled and his bloody clothes were found hidden in the attic. It emerged Celine had died from blows to the head with a brick.
The model prisoner was last year temporarily moved to the plush Shelton Abbey open prison, reserved for low-risk inmates coming to the end of their sentences. The 56 inmates live in dormitory-style accommodation and spend their days gardening and growing flowers.
Each year timber is cut on the grounds and sold in aid of St. Vincent de Paul. Lillis spent his time in the prisons taking literacy and art classes.
It is understood he will be freed in the coming two days.
It is also believed Lillis will pocket a princely €1.3m when he is let go.
The house where he murdered his wife was sold for around €1 million and legally he is entitled to half of the proceeds. He was handed a cheque in October 2012. In addition to his share of the family home he also netted €358,505 after the television production company he founded with his wife was liquidated.
He also pocketed a €400,000 pension from the business, €131,500 from the sale of an investment property in Sutton and €22,000 in investment bonds. He will be free to access the money in his bank account when he is released and can do whatever he wishes with it.
Following Lillis' conviction for manslaughter, his daughter Georgia and Celine's brother and sister fought and lost a High Court case to prevent him from getting half of the couple's assets because he was responsible for killing her.