The Court of Appeal on Wednesday denied bail for Jatupat Boonpattararaksa so he could work with lawyers outside the prison to prepare his defence against charges of lese majeste.
The Region 4 court backed the Khon Kaen Provincial Court, which had rejected bail requests filed on behalf of Mr Jatupat, better known as "Pai Dao Din", ruling that he had shown no sign of ending his damaging criticism of the country.
The student activist from Khon Kaen University was indicted on Feb 10 by prosecutors in the northeastern province for alleged lese majeste and violation of the Computer Crime Act.
He was charged after sharing a BBC Thai article on the life of His Majesty the King on his Facebook page on Dec 2.
He has denied all allegations and the court set March 21 for the pretrial examination of evidence and witness lists.
His lawyers have tried to convince the court to allow his temporarily release from the provincial prison to help them prepare his defence.
Mr Jatupat insisted on his innocence before the court on Wednesday, and said he had difficulty preparing his defence while he remained in jail.
Athipong Phuphiew, one of his lawyers, said the team will work with human rights advocates in making preparations for the trial.