A wealthy American client of UBS is expected to plead guilty on Thursday to criminal charges of tax fraud, according to persons briefed on the matter. It is the latest victory for the government in its crackdown on UBS and its offshore private banking accounts.

The client, Steven Michael Rubinstein, an accountant involved in the yacht industry, will enter a guilty plea in federal court in Fort Lauderdale, Fla., and agree to cooperate with the government’s continuing investigation into scores of UBS clients over offshore tax evasion, according to the people briefed on the matter.

Mr. Rubinstein was the first American client of UBS to be arrested, last April in Boca Raton, Fla., when he was charged with one criminal count of filing a false and fraudulent tax return. He later pleaded not guilty but will reverse that original plea.

UBS, the world’s largest private bank, admitted in February to conspiracy to defraud the Internal Revenue Service by helping scores of wealthy Americans hide nearly $20 billion overseas.

The bank paid $780 million to settle the charges, but it remains under investigation, as do its American clients, whom prosecutors have pledged to pursue. The admission has helped to open the world of offshore banking and dealt a death blow to Swiss financial secrecy.

Mr. Rubinstein worked for an international company, most recently out of Coral Gables, Fla., that helped wealthy Americans buy, sell and build yachts.

His name was among 285 that UBS turned over in February as part of its settlement.