While Trump's election in the USA and the surprise triumph of Brexit in the United Kingdom has forced France to come to terms with the possibility of an unprecedented victory by the radical right, Fillon securing the nomination may complicateLe Pen's path the presidency.
Fillon was on his way to a commanding victory, capping a tumultuous week that nixed long-established predictions.
Odoxa showed Fillon winning the first round by 10 points from Le Pen and then trouncing her 71 per cent to 20 per cent in the runoff.
Fillon, a self-professed Thatcherite, is depicted in Germany like a French version of former German chancellor Gerhard Schroeder, who drove home painful social welfare reforms in the early 2000s.
Mr Fillon has also vowed to cut 500,000 public sector jobs, while reducing public spending, taxes and regulations on businesses in order to support entrepreneurs. "It wants truth and it wants action", Mr Fillon said at his campaign headquarters as he accepted the nomination.
Based on results from about 88% of polling stations, organisers of the centre-right Republicans party primary said Mr Fillon led with 67% of the vote compared to 33% for Mr Juppe.
Sarkozy, who lost power to Socialist Francois Hollande in 2012 and failed to make it to the runoff of his party's primary for a 2017 contender, once described Fillon as little more than a member of staff, calling him in French his "collaborateur".
Prime Minister Manuel Valls said on Sunday that he would not rule out running against Mr Hollande in the primary, telling the Journal du Dimanche he wanted to dispel the idea "that the left has no chance" of retaining power.
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"My choice is Francois Fillon because I don't want a right that is tainted by the left", said Harold Bakinsian, a 51 year-old architect voting in Frejus on the Mediterranean coast.
Hollande's former protege and economy minister, 38-year-old Emmanuel Macron, is also set to stand for the presidency as a centrist independent.
"This past presidential term has been pathetic", Fillon said in criticizing Hollande.
Fillon walked a careful line Sunday, stressing the need for "authority of the state" but also insisting, "No one should feel excluded from a society that I want to see more just and with more solidarity".
While he's seen as lacking charisma, Fillon's supporters like him because they regard him as experienced and well-qualified for France's top job.
Next year's presidentials in the euro zone's second-largest economy are shaping up to be another test of the strength of anti-establishment parties in Western countries, with French voters angry with stubbornly high unemployment and fearful after a wave of Islamist militant Attacks.
Socialist Party candidates now have to announce their intention to run before 15 December and their first primary is held on 22 January.
Far-right leader Marine Le Pen was already on the attack on Sunday, saying: "No candidate has ever gone so far in bowing to the ultra-liberal demands of the European Union".
The party's deputy leader, Florian Philippot [flor-ee-AHN fil-ip-O], says Mr Fillon's economic program is harsh, and his views are outdated and won't be supported by the French people.