Lee Jae-Yong was arrested on February 17, 2017, on suspicion of bribery, embezzlement and perjury.
He and four senior Samsung executives were later charged with involvement in a giant corruption scandal involving South Korean President Park Geun-Hye and her immediate entourage.
Yae-Yong and the other leaders were suspected of hiding the president's assets and of bribing the president in exchange for political support.
At the center was also the president's close friend and adviser Choi Soon-Sil, who became rich through donations from several companies.
Samsung is said to have donated three competition horses to Choi Soon-Sil's daughter.
Convicted again
Jae-Yong was sentenced to prison in August 2017 for, among other things, bribery, but was released six months later after his prison sentence was shortened.
The verdict was appealed to the South Korean Supreme Court and now comes the new verdict.
Jae-Yong is again convicted of bribery and must now serve a 2.5-year prison sentence.
According to the Supreme Court, the previous ruling did not take into account all the bribes that were part of the corruption scandal.
The president was deposed
The then President Park Geun-Hye was deposed in a Supreme Court indictment in 2017 after a long series of bribery scandals were discovered.
She had received huge bribes from large corporate groups, including Samsung.
Lee Jae-Yong is Deputy Chairman of Samsung Electronics and son of the Group's Chairman Lee Kun-Hee.
In practice, Lee Jae-Yong has run the company since his father's heart attack in 2014.