The 31-year-old maths teacher had an affair for several months with the girl this year after they struck up a conversation on Instagram.
The pupil, who was in the man's class last year, insisted the pair were in love but her parents said he was a sexual predator who exploited his position of power.
The girl later told the court that she thought she had been "manipulated".
The man was given an 18-month suspended sentence by a court in Fontainebleau outside Paris after he was found guilty of sexually assaulting a minor aged under 15 while in a position of authority.
He has been banned from working with minors.
"I was completely out of control, I have no excuse," he admitted in court.
"When I was with her she was just my girlfriend, not my pupil and not a 14-year-old girl," he said.
There is no minimum age of consent in France, which does not treat sex between an adult and a minor as rape unless there is proof of force.
The government has promised to change the law after a man was acquitted of rape earlier this month, as the jury found no evidence he had forced an 11-year-old girl to have sex.
Currently, sex with a minor aged under 15 is classified as sexual assault, punishable by up to five years in prison.
Adults wielding some form of authority over the child face heavier sentences.
President Emmanuel Macron said he wanted a minimum age of consent of 15, in a speech on sexism to mark the UN's International Day for the Elimination of Violence Against Women.
First lady Brigitte Macron, who was once the president's drama teacher, has also vowed to play a part in combatting sexual crimes and sexism, after a wave of abuse claims worldwide.