Stuart Gibson, US justice department lawyer, said that both parties have settled on the details of a contract.
However, Mr Gibson added that it will "take a little time for the agreements to be signed in final form".
Details of the arrangement, such as how many names of the US customers that hold offshore accounts at UBS will be revealed to the government, were not divulged.
Florida-based tax lawyer William Sharp told the Associated Press that it is unlikely that such a move would have been made without a "substantial handover" of details.
He predicted that "at least several hundred, if not thousands" of names have been supplied to the authorities.
Shares in UBS fell earlier this week due to the ongoing negotiations, but have now rebounded on the news.