The left-winger has also urged people to take to the streets to protest against his pro-business agenda.
The army chief said that the president’s fiercest critic was not a “useful” political opponent.
Mrs Parly told Europe 1 radio: “Mr Mélenchon is calling into question the legitimacy of the presidential election results.
“We have a president (who won a democratic election and) whose party won an absolute majority in parliament in legislative elections five months ago.
“And yet Mr Mélenchon is constantly calling into question universal suffrage… he’s speaking outside the democratic framework, which is shocking.”
Mrs Parly also accused Mr Mélenchon of hypocrisy, saying the far-left MP had branded Mr Macron’s tough reforms a “social coup d’état” when in fact the reforms designed to deeply transform France had “always been” a key part of the president’s political programme.
He said: ”Mr Mélenchon is calling for people opposed to the government’s reform plans to take to the streets in protest, because, according to him, democracy is the street.
“And protesting is a right in any democratic society. But the way I see things is that the street is what helped propel Hitler to power.
“Mr Mélenchon is not a useful opponent. He wants to make a lot of noise, and he is making a lot of noise. But he’s not being useful. A healthy democracy needs a strong – but useful – opposition.”
Mr Mélenchon, the head of the Communist-backed La France Insoumise (France Unbowed) party, sparked outrage last month after he said at a mass demonstration against the labour code reform that ‘the street’ had “toppled France’s kings” and “driven out the Nazis”.
The far-left MP was responding to an earlier claim by the president that “democracy is not the street,” but faced a torrent of condemnation after Mr Macron’s camp accused him of comparing the current government to the Nazi regime, an accusation he vehemently denied.