Sarkozy, the former prime minister of France and the leader of the centre-right Republicans, made the comments during a speech in Rochefort, south western France, on Tuesday night.
“To the millions of French people who voted for the National Front… a vote for the National Front is not a vote against the Republic, it is not immoral,” he said.
He added that if it was “immoral” to do so, then France “wouldn't have tolerated National Front candidates for the last 30 years”.
He followed the comments with an attack on the National Front's capabilities of running regions, saying giving power to people “who have never governed anything” can only result in “chaos”.
Sarkozy added that many voters had chosen the National Front because they were feeling frustration and anxiety, and had “reacted without thinking” while at the polls.
The first round of the regional elections over the weekend saw unprecedented success for the National Front, with the party pulling in around 6 million votes – nearly 28 percent of the total.
It topped the polls in six of the country's 13 regions, and looks set to win control of at least two regions in the second round of voting this Sunday.
Following Sunday night's shock, Nicolas Sarkozy and his centre-right Republicans party have refused to countenance any kind of deals with the rival Socialist party in order to keep the National Front out of power.
French political analyst Bruno Cautres told The Local earlier this week
it was indeed thanks to Marine Le Pen and the National Front that the Republicans suffered.
“They just did not perform as well as expected and it shows the Republicans party is really under pressure from the National Front,” he said.
“Sarkozy used to be good at attracting the National Front voters, but today we see the opposite is happening.”
If, however, voters unite to keep out the far right on Sunday, it will be Sarkozy and the Republicans who will benefit.
'The National Front is a scam'
France's Socialist PM Manuel Valls also tried to win back voters from the National Front, saying he respected them, but the party they voted for was a scam.
“I respect all the Front National voters,” said Manuel Valls. “But they are wrong, they are being deceived by this scam.”
“I say to my compatriots, do not fall for the National Front’s trick. I don’t want my country to go looking for an extreme solution.”
“Leaving the euro, it’s a con, it would bring the country to its knees. And all those who are sometimes seduced by the National Front; the workers, the pensioners, traders, they would all be ruined.
“It’s a scam. The National Front talk of security but in the National Assembly and the Senate, they never back any measure to fight against terrorism.”