The issue has divided the French parliament but the vote to extend Operation Sangaris, whose mandate is due to expire in April, is expected to pass in both houses.
"If Operation Sangaris had not been launched there would have been genocide in the Central African Republic," Fabius said on France 2 television.
"The French were right to intervene," he said of the mission launched in December.
"We did it with the Africans of MISCA (the African Union force) and now the Europeans are coming to help us."
The number of French peacekeepers is expected to rise from 1,600 to 2,000 to support a 6,000-strong African Union force.
The European Union plans to send 1,000 troops to the strife-torn country. A French minister said the deployment would start next month.
The impoverished country descended into chaos last March after a rebellion overthrew the government, sparking deadly violence between the Christian majority and Muslim minority that has uprooted around a million people out of a population of 4.6 million.
The head of Sangaris, General Francisco Soriano, said on Monday that the French intervention had helped improve security and denied allegations by Amnesty International that ethnic cleansing was taking place in the country.
But despite the government's defence of the mission, opposition lawmakers alleged that there had been little success on the ground.
"Nothing has been resolved, the country is still on fire," said former minister Eric Woerth, a lawmaker from the centre-right UMP party of ex-president Nicolas Sarkozy.
"We have avoided a bloodbath, a massacre," Woerth said, but added that there is "no state, no judiciary, no police, no schools" in the former French colony.
A campaign of abuses by the mainly Muslim ex-rebels led to revenge killings by Christian militias, in sectarian violence that French and African troops have failed to stem nearly three months on.
Rebel leader Michel Djotodia, the country's first Muslim leader, was forced to step down last month under regional pressure after failing to stop the atrocities that have left thousands dead.
Clashes broke out again at the weekend between MISCA soldiers and mainly Christian militias known as "anti-balaka" (anti-machete). Two Chadian soldiers and two anti-balaka fighters were killed on Sunday.