"This person was on Ukrainian territory illegally and therefore, in compliance with all legal procedures, he was returned to the country from where he arrived", Ukraine's border service stated.
The State Border Guard Service said he was removed from Ukraine on February 12 because he was in the country illegally.
He was permitted into Poland as the spouse of a European Union citizen, the Polish guards said.
Saakashvili has campaigned feverishly for the impeachment of Ukrainian President Petro Poroshenko since resigning his position of governor of Odessa, citing corruption at the top levels of the Ukrainian government.
In January 2018, the court of Kyiv dismissed Saakashvili's appeal to the State Migration Service, asking to recognize him a refugee. Saakashvili believes that Poroshenko's decision to deprive him of Ukrainian citizenship in summer 2017 was illegal.
Saakashvili spent his first years in office as the toast of the Neo-Conservatives in the George W. Bush administration.
A number of criminal cases were opened against Saakashvili in Georgia, which has been seeking his extradition from Ukraine for a long time.More news: Statue of Liberty cleared for USA helmets
By 2007, however, he began falling out of favour with many of his foreign backers and local supporters because of his wildly eccentric and often impulsive behaviour.
He said he had given up his Georgian citizenship.
Saakashvili is also wanted in Georgia for multiple charges.
He also alleged that his Georgian bodyguards, friends and supporters had been kidnapped by Ukrainian security services, tortured and deported to Georgia in recent months.
Upon his arrival in Poland, Saakashvili said his deportation showed Poroshenko's weakness.
However, their relationship deteriorated, culminating in Saakashvili's resignation from the position in 2016 in a protest against what he said was high-level corruption.
"There will be a big protest of Ukraine's united opposition on February 18".
The controversial politician then vowed to challenge the Ukrainian government.