Former Georgian President Mikheil Saakashvili has been appointed governor of Ukraine's southern Odessa region.
Announcing the surprise move in the Black Sea port of Odessa, President Petro Poroshenko said Mr Saakashvili had been granted Ukrainian citizenship.
Mr Saakashvili is widely credited with carrying out radical reforms in Georgia during his terms in office in 2004-13.
However, current Georgian authorities accuse him of abuse of power and have demanded his extradition.
Mr Saakashvili left Georgia after his term as president ended in 2013. He denies the charges against him, which he says are politically motivated.
Analysis: David Stern, BBC News, Kiev
The complete surprise of Mikheil Saakashvili's appointment as Odessa governor has left a large number of political observers at a loss for an explanation.
President Petro Poroshenko's reasons will be come clearer with time, but at the moment, many are struggling to see the strategy behind naming a former leader of another country to run a provincial government.
Saakashvili is a political outsider, with few ties to the Odessa region, and comes with a reputation for divisiveness and a high level of self-involvement.
But he is also pro-Western, pro-reform and apparently very loyal to Mr Poroshenko - which will come in handy if he takes on local corruption and vested interests, as Mr Poroshenko apparently wants.
The move could be a stroke of genius on Mr Poroshenko's part - or a blunder of breathtaking magnitude. At the very least, it points to his lack of choices among home-grown candidates.
President Poroshenko made the announcement at a televised event in Odessa, with Mr Saakashvili standing beside him.
"We are united by our love of Odessa and Ukraine," Mr Poroshenko said, adding that that the new governor would bring in discipline and carry out much needed reforms.
"In just one year, Oddessites should feel that their living standards are higher."
The Ukrainian president also said his decision was part of his drive to limit the political influence of the country's oligarchs.
Russian Prime Minister Dmitriy Medvedev later made sarcastic comments on the appointment, describing it as a "Chapiteau-show" - in a reference to a popular Russian farcical comedy.
Moscow has been highly critical of Mr Saakashvili since Georgia and Russia fought a brief war in 2008.
Unlike Ukraine's eastern Donetsk and Luhansk regions, Odessa has not been hit by the fighting between government forces and pro-Russian rebels.
However, tensions in the strategic port remain high after clashes between pro- and anti-government protesters on 2 May 2014 left more than 40 people dead.
The majority of those who died were pro-Russian activists who perished in a fire in a trade union building. Investigations into what caused the blaze are continuing.
The Ukrainian government, Western leaders and Nato all say there is clear evidence that Russia is helping the rebels in the east with heavy weapons and soldiers. Independent experts echo that accusation.
Moscow denies it, insisting that any Russians serving with the rebels are volunteers.
More than 6,000 people have been killed in fighting in eastern Ukraine that began in April 2014 when rebels seized large parts of the Donetsk and Luhansk regions. This followed Russia's annexation of the Crimea peninsula.