Giovanni Di Stefano, 57, conned clients out of large sums of money by setting himself up as a lawyer when he had no legal qualifications and was not registered to work as a lawyer in Italy or Britain.
During the trial, the court heard Di Stefano had links to Zimbabwe's President Robert Mugabe, al Qaeda founder Osama bin Laden, late Serbian strongman Slobodan Milosevic and Saddam.
The court was shown a BBC documentary from 2004 in which he described Saddam as a "nice guy" and boasted of being asked to defend a number of notorious British killers such as Harold Shipman, the family doctor who murdered about 250 patients.
Prosecuting lawyer David Aaronberg said he had gained a reputation which brought him "the fame, or the notoriety, that he enjoys".
"He was a man who was willing to provide legal services to clients whose cases others considered unwinnable or too difficult to defend," Aaronberg said.
Di Stefano was found guilty at Southwark Crown Court of 25 offences of deception, fraud, money laundering and forgery allegedly committed between 2004 and 2012, British news agency the Press Association reported.
Di Stefano, who was born in the small town of Petrella Tifernina in central Italy but moved to Britain as a boy, will be sentenced on Thursday.