ROME—Italy's highest court on Thursday threw out the long-running corruption trial of David Mills, a former lawyer of Prime Minister Silvio Berlusconi, in a move that casts doubt over whether a related corruption trial facing the Italian leader will reach a conclusion.

Messrs. Mills and Berlusconi have been facing separate, but related, corruption trials. At the heart of both cases is a $600,000 payment Mr. Berlusconi allegedly made to Mr. Mills in the late 1990s, allegedly so the lawyer would give false testimony to help the Italian billionaire and his Fininvest media empire during two trials of Mr. Berlusconi at the time. Mr. Berlusconi was acquitted in one of those trials; in the other, the statute of limitations ran out, and the case was dropped.

In its ruling, which is final and can't be appealed, the high court said Mr. Mills had received the payment. However, the judges found that lower courts—which had originally convicted Mr. Mills—had improperly interpreted the statute of limitations in the case. Therefore, they threw the case out.

"I am very relieved that this saga has finally now come to an end and happy to be able to get back to a normal life again," Mr. Mills said in a statement. Mr. Mills is the estranged husband of U.K. Labour Party politician Tessa Jowell, a former minister in Tony Blair's government.

Mr. Berlusconi is also on trial for alleged tax fraud stemming from arrangements he allegedly made to buy film rights in the 1990s on behalf of his Mediaset TV network. Prosecutors allege that Mediaset bought the film rights at inflated rates, allowing the company to lower its tax payments. Mr. Berlusconi has repeatedly denied the charges in that case.

In February 2009, a lower court found Mr. Mills guilty of corruption, and sentenced the lawyer to four and a half years in prison for receiving the payment in 2000—which was years after the alleged false testimony. That ruling was upheld in October 2009.

The timing of the payment, as specified by the lower courts, was important because it laid out when the statute of limitations on the corruption charges would kick in. That was significant because Mr. Berlusconi's trial focused on the same corruption allegations.

Mr. Berlusconi has always maintained his innocence in the case, saying he never arranged for any payment.

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