BUCHAREST, Romania — Romania’s highest court Thursday sentenced Liviu Dragnea, the leader of the country’s governing Social Democratic Party, to three years and six months in jail for abuse of office.

While the verdict is likely to be appealed, it was a bitter blow to Mr. Dragnea, who many consider to be the most powerful politician in the country.

The High Court of Cassation and Justice found Mr. Dragnea guilty of intervening to keep two of his party’s employees, who performed no state work, on the public payroll from 2006 to 2013 when he was a local council leader. The court cleared him of a separate charge of intellectual forgery.

The verdict came in the face of escalating attacks by Mr. Dragnea and his supporters on the justice system and claims that he was the victim of a “parallel state” cabal.