The lawyer was absent when the Supreme Court on Wednesday read out its ruling against his colleagues: Pichit Chuenban and Supasri Srisawat and sent them to jail.
The court issued a warrant for Thana's arrest, but it was later discovered that he had been admitted to Bamrungrad Hospital for stress.
On Monday, when his doctors agreed that Thana's condition improved, police accompanied him from the hospital to the Supreme Court. The court read out its verdict, giving him six months' imprisonment, the same penalty as the two other defendants in the case.
Thana, who wore sunglasses and a cap to conceal his face, was later handed over to Corrections Department officials and taken to the Bangkok Remand Prison.
Wanchai Rujanawong, director-general of the Corrections Department, said Thana would be in the same detention area as his colleague Pichit. That area is for convicts facing imprisonment of no longer than six months, Wanchai explained.
The case against the trio was in connection with an allegation that Thana gave a paper bag filled with Bt2 million in cash to a court official who dealt with a separate court case against their boss Thaksin. Thana claimed that it was a matter of mix-up as his driver picked up a wrong bag instead of the one containing a gift of chocolates.
Thana, Pichit and Supasri have also been accused of bribing an official.