"Mario was in the last stages of terminal lung cancer and decided to end his long battle of suffering," it said in a statement. "This was a positive and very conscious decision on his part. He did not want to suffer anymore, nor did his family too."
'He did not want to suffer anymore, nor did his family too'
Oriani-Ambrosini died at his home in Cape Town in the early hours of Saturday morning. He was aged 53.
When asked whether Oriani-Ambrosini took his own life, the family responded with "he decided to end his suffering". They could not provide further details.
His family said they respected his decision.
"This choice was made not out of weakness, fear or despair, but from his courage or determination to be the final decision maker concerning his own fate," it said.
"We only love and respect him... more for his bravery in the face of debilitating and ultimately fatal illness."
It said Oriani-Ambrosini said in his last message to the family that he felt he had completed his life cycle.
"He told us: 'I am dying in peace and serenity, surrounded by the love of my family and friends. I am dying at a time when I feel ready. Thank you for your friendship and love which I feel with me at this time'.".
The IFP said on Monday night it was not aware of Oriani-Ambrosini's decision.
"I am not aware of such...it's the first time I hear about it," said IFP chairman Blessed Gwala.
His illness was first made public in May last year, which he described as a stage four lung cancer which, left untreated, "will cause me to be removed from all lists for Christmas functions or gifts".
He survived the 2013 festive season and vowed to fight during the fifth Parliament for the use of alternative cancer therapies, including medical marijuana.
Oriani-Ambrosini said he had rejected chemotherapy as a treatment option, as it would extend his life expectancy by only a few months and would cause severe side-effects. He had opted to pursue treatment based on "different science".
In February, he introduced the Medical Innovation Bill to legalise the use of medical marijuana and pleaded to President Jacob Zuma to provide laws that gave doctors the power to prescribe alternative treatments.
Three months later, a very frail Ambrosini lifted himself out of his wheelchair with the help of an ornate walking stick a year after announcing his diagnosis and read the oath of Parliament in his thick Italian accent.