Franceso Galdeli, 56, and Vanja Goffi, 45, were arrested on Saturday having been wanted on an Interpol red notice since 2013.
Galdeli is accused of various scams and frauds in Italy, including impersonating the Hollywood actor “to trick people into sending money”.
Mr Clooney sued the 56-year-old in 2010, telling an Italian court he never approved any affiliation with the bogus brand "GC Exclusive by George Clooney".
Galdeli was arrested on Saturday near the Thai city of Pattaya on suspicion of staying in the country illegally, while his wife was arrested on suspicion for overstaying her visa.
Thailand's crime suppression division issued a statement following the arrests, saying: "During interrogation, Francesco confessed to claiming to be George Clooney and opening a clothes business to trick people into sending money.”
Galdeli was sentenced to more than eight years in jail by a Milan court in 2010 after being found guilty of impersonating the actor to trick investors, but he fled the country.
The couple – dubbed the Italian Bonnie and Clyde – had been living in Thailand since 2014 and had overstayed their visas, authorities said.
They sustained their life in Thailand by selling fake Rolex watches online, according to Italian Media.
Police said the couple do not yet have a lawyer and will be charged for overstaying their visas before extradition proceedings begin.