Ronnie Campbell, 53, was stopped in a taxi with the drugs in November 2006.
Campbell, whose daughter is married to former Home Secretary and Celtic chairman John Reid's son, was caught as he was driven around various locations in Lanarkshire after collecting the drugs.
He had gone on trial for the offences last year but the case was abandoned after his lawyer withdrew from the case.
This week he sat in the dock at Hamilton Sheriff Court and was found guilty after a trial.
Campbell denied he was drug dealing and claimed he had been on his way to collect football tickets when he was arrested.
The jury heard how officers who searched Campbell's home in Bellshill, North Lanarkshire, had discovered £5300 and a bag with white powder in it.
Campbell's daughter Melissa wed Dr Reid's son Mark in London's Westminster Cathedral in September 2005.
At the wedding, Campbell had heavily bandaged arms and legs as he walked his daughter down the aisle after being attacked by underworld figures. There was a warrant out for his arrest at the time.
Campbell was found guilty by a majority verdict of being concerned in supplying amphetamine on November 20, 2006.
Sheriff John Miller deferred sentence until October 30.