Francis Nsiangangu, 31, who was known as Casper, died after being stabbed at least twice in Tower Hill, Brentwood, in September last year.
Bernard Ampaw, 19, of Wombridge Road, Telford, Shropshire, was convicted of murder and robbery following a trial at Chelmsford Crown Court.
Two other men were cleared of murder. Ampaw will be sentenced next month.
During the seven-week trial, the court heard Mr Nsiangangu was actively involved in the supply of cannabis.
His attackers ran off with his backpack, which contained cannabis, before he collapsed and died on the pavement.
Clive Mundoma, 19, formerly of High Street, Brentwood, was found guilty of robbery but not guilty of murder.  Along with Ampaw, he was warned by Judge Charles Gratwicke to expect a long sentence.
Wilson Lourenco, 19, of Cheviot Gardens, Chelmsford, was acquitted of murder and robbery.
A man has been found guilty of the murder and robbery of a college student "when a drug deal went wrong" in Essex.