Fake Sheikh Mazher Mahmood could be facing jail later for tampering with evidence in the collapsed drugs trial of pop star Tulisa Contostavlos.
Following a two-week trial at the Old Bailey, a jury found the 53-year-old "King of the Sting" and his driver, Alan Smith, 67, guilty of plotting to pervert the course of justice.
The trial had heard that Mahmood and Smith conspired to suppress evidence in the N-Dubz star's trial, which was thrown out at Southwark Crown Court in July 2014.
The singer had been accused of arranging for Mahmood to be sold £800 of cocaine by one of her contacts following an elaborate sting for The Sun on Sunday in May 2013.
During a meeting at the Metropolitan Hotel in London, Mahmood posed as a film producer and plied Miss Contostavlos with alcohol as they discussed an acting role alongside Hollywood star Leonardo DiCaprio.
As Smith drove the former X Factor judge home to Hertfordshire, she allegedly spoke about a family member who had a drugs problem.
When he was interviewed by police about the journey more than a year later, Smith, of Dereham, Norfolk, recalled the conversation.
But a day later, after speaking to Mahmood and emailing his draft statement, the singer's anti-drugs comments were removed, the court heard.
At a pre-trial hearing, Mahmood denied being an "agent provocateur" or that he discussed the drugs conversation with Smith.
But when he was questioned at length in the trial, Mahmood appeared to concede he had talked to Smith about what Miss Contostavlos said about drugs in the car. The case was subsequently thrown out.
Neither defendant gave evidence but it was said on Mahmood's behalf that there had been a "misunderstanding" of his evidence as he was "steamrollered" with multi-faceted questions.
And Miss Contostavlos's comments in the car would not have stacked up against the "clear and incontrovertible evidence" against her, it was claimed.
Defence lawyer John Kelsey-Fry QC told jurors: "Mr Mahmood is not a policeman. He is a journalist.
"Whilst the prosecution may say he boasts of the number of convictions resulting from his work, securing convictions is not actually his job."
He said Mahmood's whole investigation was about exposing the pop star's private face "smoking weed" and "arranging cocaine for mates" set against her public persona as a "role model".
Following the guilty verdicts, it was announced that 18 civil claims were being launched against Mahmood which could total some £800 million.
For more than 25 years, Mahmood has enjoyed a position as "King of the Sting" at the now defunct News of the World, Sunday Times and Sun on Sunday, with Smith as his "right-hand man".
He claims to have helped put more than 100 criminals behind bars and risked his life on a daily basis to lift the lid on the murky world of crime.
Paedophiles, arms dealers and drug dealers have all found themselves at the centre of his stories, as have celebrities and public figures, including the Countess of Wessex, who was taped calling the Queen ''the old dear'', and Sven-Goran Eriksson, who revealed his plans to quit as England head football coach.
After her case collapsed in July 2014, Miss Contostavlos claimed to reporters she had been the victim of ''a horrific and disgusting entrapment''.
The Crown Prosecution Service has since dropped a number of live cases and reviewed 25 past convictions.
Six of those involving mainly high-profile individuals have been taken up by the Criminal Cases Review Commission.
Judge Gerald Gordon will sentence Mahmood and Smith from 11am at the Old Bailey. Both defendants are on bail.
Mahmood, from Purley, south London, has been suspended by News UK since the collapse of the Tulisa trial.