London's Metropolitan Police said Domenico Rancadore, 64, had been arrested yesterday on a European arrest warrant.
Considered an important member of the Sicilian mafia group Cosa Nostra, he has been wanted by Italian police for 19 years and is on Rome's list of most dangerous criminals.
He has an outstanding prison sentence of seven years in Italy for mafia-related activities, according to the arrest warrant.
"He was taken into police custody and is scheduled to appear at Westminster Magistrates' Court today (8 August)," police said in a statement.
His prison sentence relates to mafia activities between 1987 and 1995 in Palermo, the main city on the island of Sicily, according to the arrest warrant.
An international arrest warrant for Rancadore was issued in 1998.
