He denied the two charges but pleaded guilty to money laundering.
His brother, Simon McFadden, 41, was found guilty of conspiring to supply. Simon’s wife Karen McFadden pleaded guilty to money laundering.
After the verdict, Det Ch Insp Nick Wallen, of West Yorkshire Police, said McFadden “was, in fact, a criminal purporting to be a police officer”.
“Some police officers, Nicholas McFadden’s former colleagues, had risked their lives to take drugs off the streets, and he, along with his brother, was putting them back there,” he said.
Nicholas McFadden, 38, of Church Avenue, Leeds, worked for a special organised crime group and was in charge of looking after evidence, the jury was told.
Leeds Crown Court heard the detective constable, who joined the force in 2000, helped himself to heroin, cocaine and cannabis by exploiting “slack” procedures at secret evidence stores.
‘Reacted swiftly’When police raided his family home in Castleford they found almost £160,000 in banknotes stuffed into sacks in his garage, and £20,000 hidden around his house. They also discovered £6,000 in his performance car.
The 38-year-old, who claimed he stole the cash from a drug dealer and made money selling illegal steroids, was acquitted on a charge of stealing amphetamine and the jury found both the brothers not guilty of conspiring to supply it.
The former detective was caught after regularly paying cash into automatic banking machines which triggered a security alert, the court was told.
When he was arrested, he told police he found bags of cash in a ditch by the M62 motorway.
The court was told large amounts of cash, along with mobile phones that contained messages about drug deals, were found at Simon McFadden’s terraced home during a search.
Simon McFadden, of Darfield Place, Harehills, Leeds, denied conspiracy to supply.
His wife Karen McFadden, who has a teenage son with her husband, did not appear in the dock during the trial.
She is due to be sentenced with the two brothers at Leeds Crown Court on Thursday.
West Yorkshire Police said it had reacted swiftly when it became aware of McFadden’s activities and carried out a meticulous investigation which led to the convictions.