The estranged couple, who split in November 2011, have allegedly signed the necessary paperwork to dissolve their six year marriage.
It is thought that the divorce was delayed by disagreements about finances.
According to reports, 50-year-old Demi - estimated to be worth more than £100 million – was asking for spousal support from her ex, who became the highest-paid actor on TV when he replaced Charlie Sheen as the leading role in Two And A Half Men in May 2011 .
"There had been lengthy negotiations between lawyers for both sides about the financial settlement – in particular how much he owed her from their marriage," an insider added.
"They have finally come to an agreement that was acceptable to all sides."
Ashton, 35, and Demi - who tied the knot in September 2005 - appeared to be on friendly terms when they were spotted amiably chatting at Burbank Airport two months ago.
Since splitting from Demi, Ashton has moved on with Black Swan beauty Mila Kunis, while Demi was most recently linked to 30-year-old Australian pearl diver Will Hanigan.