Mirza Fakhrul Islam Alamgir is secretary general of the Bangladesh Nationalist Party (BNP).
"He (Alamgir) was released from the (specialised) Bangabandhu Sheikh Mujib Medical College Medical University Hospital this evening as the Supreme Court order reached us this evening," an official of Dhaka Central Jail said.
The apex court earlier granted him six weeks' bail to avail "advanced medical treatment" as Alamgir was being treated at the facility under the custody of prison authorities.
"I am sick, suffering from cardiac ailments. I will serve the people of my country after returning from abroad," Alamgir said as he walked out of the hospital.
Police in riot gears and plainclothes barged into Alamgir's car as he came out of the National Press Club premises after an overnight stay inside seeking to evade arrest.