Several hundred supporters demonstrated near the court and some threw plastic bottles and rubbish at police in protest after the verdicts and sentences were announced.
Prosecutors had charged Chen with embezzling more than $3m from a presidential office fund, accepting bribes of about $9m related to a land procurement deal and taking another $2.7m in return for helping a contractor win its bid for a government project.
Chen, who frequently angered China with his pro-independence rhetoric during his term, is the island’s first former leader to be arrested, charged and tried.
He accused his successor, Ma Ying-jeou, of leading a politically motivated “witch hunt” against him, which Ma has denied.
Chen, who says he is being punished for advocating Taiwanese independence, has gone on hunger strike three times and dismissed his lawyers in protest against his detention and trial.
Some legal experts have expressed concern about the handling of the case, including the court’s decision to detain Chen before his trial and to switch the presiding judge.
In a letter to the Taiwan government earlier this year, nearly 30 international scholars warned that “the erosion of the judicial system” could jeopardise Chen’s right to a fair trial.
Taiwan has been governed separately from China since 1949, and Chen spent his presidency pushing for formal independence, angering China, which sees the country as part of its territory.