Writing in the Sunday Mirror, Prescott agreed with former UN secretary general Kofi Annan's assertion that the Iraq War was "illegal", as its primary aim was regime change.
The ex-deputy PM, who supported Tony Blair's decision to join the US-led invasion of Iraq in 2003, said he would take his "fair share of the blame" for the consequences of the conflict.
"A day doesn't go by when I don't think of the decision we made to go to war," he wrote.
"Of the British troops who gave their lives or suffered injuries for their country. Of the 175,000 civilians who died from the Pandora's Box we opened by removing Saddam Hussein.
"I will live with the decision of going to war and its catastrophic consequences for the rest of my life."
'Not enough documentation'
Prescott accused Blair of running his government like a shadow cabinet, saying that too little paper documentation was given to ministers to arrive at key decisions before the invasion.
He was also critical of the lack of written reasoning when the then attorney general, Lord Goldsmith, proclaimed to cabinet ministers that it was legal to act militarily against Iraq.
"The timing of the decision was clearly designed to endorse an almost immediate action for us to go to war," Prescott wrote.
"In my evidence to Chilcot, I said the attorney general in the weeks before the decision was an 'unhappy bunny' as he continued to find a justification to invade Iraq."
The Chilcot report, released on 6 July, stopped short of calling the Iraq War illegal but was highly critical of the government's decision-making process before the invasion.
It concluded that Blair had overstated the case for military action and that there was no "imminent threat" from Hussein.