Vladimir Kuznetsov, 49, was sentenced on Friday by a district court and ordered to pay a total of $73,000 in fines.
The Russian consul in New York, Sergei Garmonin, said the verdict was unjustified and that Russia would fight to uphold Kuznetsov's good name.
"The court based its verdict on the testimony of just one witness while ignoring all evidence in favor of Kuznetsov," he said.
Kuznetsov, who worked as a Russian expert in the United Nations Advisory Committee on Administrative and Budgetary Questions, was arrested in September 2005 after borrowing $300,000 from a Russian colleague, allegedly knowing that the funds had been acquired by criminal means.
He was found guilty by a jury in March.
Kuznetsov previously held diplomatic immunity as a UN employee, but after former secretary general Kofi Annan revoked the status, the FBI were able to arrest him.