Mercier, 75, who served under former president Nicolas Sarkozy between 2010 and 2012, claimed tens of thousands of euros for his wife and daughter for parliamentary jobs they never carried out.
The court handed him a suspended prison sentence of three years.
Mercier gave “personal gain precedence over the public good”, the court said in its verdict, calling Mercier’s actions “serious”.
As senator, Mercier claimed 50,000 euros ($54,000 at today’s rate) in salary for his wife Joelle between 2005 and 2009, and €37,000 for his daughter Delphine between 2012 and 2014.
During that time, Delphine Mercier was living in London and did not set foot in the French Senate, but her father claimed she was acting as his “cultural advisor”.
Neither Mercier nor his daughter were able to provide any proof of actual work done.
Joelle Mercier, meanwhile, claimed during the trial that she had served as her husband’s representative at village fairs and funerals.
She was found guilty of conspiracy to embezzle public funds and of receiving stolen money and sentenced to a suspended prison term of 18 months and a €40,000 fine.
The court handed the daughter a 12-month suspended sentence and a fine of €10,000.
Prosecutors had asked for the ex-minister to serve one year behind bars, accusing him of “creating smoke screens” in his defence and seeking to mislead the court.
Mercier had based part of his defence on his rural roots, pitting his “common sense” against the “Parisians” of the national financial crimes unit PNF.
Several French politicians have been convicted for similar offences committed before France in 2017 banned National Assembly deputies and senators from employing family members.
The move came in reaction to a public outcry over a high-profile case involving former right-wing prime minister Francois Fillon, who was found guilty of providing a fake parliamentary assistant job to his wife that saw her paid hundreds of thousands of euros in public funds.
The “Penelopegate” scandal, revealed in a media report while he was the front-runner in the 2017 presidential race, torpedoed his political career and cleared a path for then-relatively unknown Emmanuel Macron.
Last year, a court trimmed Fillon’s sentence to four years in prison with three suspended — down from five years with three suspended when he was first found guilty in 2020.