Sisters Francesca and Elisabetta Grillo had been accused of spending £685,000 ($1.12 million) on credit cards belonging to their employers without permission.
They claimed there had been a tacit understanding that Lawson would allow this to continue if they kept quiet about her alleged use of drugs.
In court, Lawson admitted taking cocaine on a number of occasions, but denied having a drug problem.
The sisters’ lawyer Richard Cannon said they were “naturally relieved” by the verdict, the BBC reported.
He added they had faced a “long, hard fight played out in the gaze of the world’s media.”
Anthony Metzer, who represented Elisabetta, said his client was “relieved” and “crying her eyes out.”