Masked officers dragged Saakashvili from an apartment in the capital, Kiev, while his supporters protested on the street and tried to stop the police van from leaving.
It is the latest twist in a prolonged feud between Ukrainian authorities and Saakashvili, who was invited to become a regional governor after protests in 2014 ousted a pro-Russian president but quickly fell out with the president, his one-time ally Petro Poroshenko.
Addressing supporters earlier from the roof of the house, Saakashvili had accused Poroshenko of being a traitor and a thief. He tried to address the crowd again as he was being bundled into a blue minivan, which was then surrounded by protesters.
“What they are doing is lawlessness in the eyes of the whole world,” Saakashvili said. “I urge all Ukrainians to take to the streets and drive out the thieves.”
Saakashvili made a dramatic return to Ukraine in September, barging his way across the border from Poland despite having been stripped of Ukrainian citizenship and facing the threat of possible extradition to Georgia.
He wants to unseat Poroshenko and replace him with a new, younger politician.
Saakashvili was appointed governor of the Odessa region in 2015 on the strength of the reforms he carried out in Georgia.
But he quit in 2016 after falling out with Poroshenko, accusing him of corruption, while Poroshenko’s office said Saakashvili was trying to deflect from his own shortcomings as an administrator.
Saakashvili divides opinion. Supporters see him as a fearless crusader against corruption but critics say there is little substance behind his blustery rhetoric.
Back home in Georgia, where he took power after a peaceful pro-western uprising, known as the Rose Revolution, in 2003, his time in office was tarnished by what critics said was his monopolizing power and exerting pressure on the judiciary.
He was president at the time of a disastrous five-day war with Russia in 2008, a conflict that his critics argued was the result of his own miscalculations.
The 49-year-old is now wanted on criminal charges in Georgia, which he says were trumped up for political reasons.