Shortly after the hearing, Saakashvili met with his supporters waiting in front of the court building.
He is charged with "assisting members of criminal organisations and concealing their criminal activity" and could face up to ten years in jail.
The court hearing drew wide media attention both in Georgia and Ukraine, as well as internationally. On December 9, prosecutors said they would ask a court to place him under house arrest with electronic monitoring pending trial.
But judge Larysa Tsokol ruled not to grant this request, letting the opposition politician go free for the duration of the probe, a decision met with applause from supporters in the courtroom and Saakashvili, who called the judge "courageous". They also have suggested that Saakashvili's protests are part of a Russian plot against Ukraine.
Tuesday's drama marked the latest chapter in the dizzying career of a man who spearheaded a pro-Western "Rose Revolution" in Georgia in 2003 and fought a disastrous war with Russian Federation five years later that eventually prompted him to flee the Caucasus country.
"I consider myself a prisoner of Ukrainian oligarchs", he said in an apparent reference to the business background of Poroshenko, who ran a chocolate business before he was elected president.More news: Donald Trump's #metoo moment is here
More news: Baker Mayfield shocks no one, wins 2017 Heisman Trophy
More news: Abbas praises global condemnation of Trump Jerusalem announcement
Saakashvili called for calm when police scuffled with supporters in the street outside and a smoke bomb was apparently thrown, saying that "we don't want confrontation".
Yulia Tymoshenko, a former prime minister who leads an opposition party, attended the hearing in a show of support for Mr Saakashvili.
"You are jailing your opponents - the way Yanukovych did".
Mr Saakashvili rejected the allegations and is refusing food to protest against his detention.
Poroshenko brought Saakashvili and his team to Ukraine in 2015, gave him the Ukrainian citizenship and appointed him as the governor of the Odessa region to use his image as the author of Georgia's successful reforms.