Archer is currently serving four years for perjury
An audit led by accountants KPMG found "no evidence of misappropriation", the British Red Cross said.
Lady Archer said she and her family were "delighted but not surprised" at the decision.
The investigation into the peer's charity work on behalf of Iraqi Kurds was sparked by a letter from Liberal Democrat peer Baroness Nicholson to Scotland Yard.
Charity concert
Sir Nicholas Young, British Red Cross chief executive, said: "I am pleased that KPMG has found no evidence of misappropriation."
He said the report explained which figures were not "sufficiently documented and which were not presented with sufficient clarity".
"We have learned from this experience," he added.
He said the Simple Truth campaign - which centred around a high profile charity concert - generated widespread support and aid.
The accusations against the millionaire novelist came out in the aftermath of his conviction and stopped him being transferred to a lower security jail.
The global appeal for the Kurds was said to have raised £57m, although there was confusion at the time over how much money a benefit concert organised by Archer had raised.
Family's delight
Lady Archer said her family was proud of the charity work her husband had done.
"My family and I are delighted, but not surprised, that KPMG's investigation into the Simple Truth campaign, spearheaded by Jeffrey in 1991, has confirmed that no funds were misappropriated by him or anyone else.
"We have known this from the outset.
"We are very proud of the work Jeffrey has done for Kurdish relief, the British Red Cross and many other good causes over the years.
"Baroness Nicholson, whose allegations have wasted much time and caused much unjustified distress, should surely now accept KPMG's findings."
Lady Archer had dismissed the allegations as "unsubstantiated and baseless" from the outset.
Accuracy
But the Fraud Squad investigated the Simple Truth fundraising campaign despite the Red Cross insisting the peer had had no control over the funds.
The former Conservative Party deputy chairman helped organise the concert at Wembley Arena for the fund in 1991.
The KPMG audit found that claims about the amount of money pledged by overseas governments "cannot be fully supported by the currently available documentation".
But it concluded there was no evidence of fraud or misappropriation and it did not question the accuracy of the British Red Cross's claim that £13.8m was raised for the fund in Britain.
"It should have been made clear in 1991 that the British Red Cross did not handle funds collected and distributed by overseas Red Cross societies," the report said.