Francois Fillon says that Europe needs reforms in the face of new global threats.
Speaking in Berlin days after US President Donald Trump's inauguration and British Prime Minister Theresa May's speech outlining her country's EU exit plans, Fillon said Europe could no longer be complacent about prosperity or stability.
"For decades we have been living under the illusion of perpetual peace," said Fillon, who polls predict would win the French election if it were held today.
"The reality is crueller," with an aggressive Russia, the threat of a trade war between the United States and China, and growing European divisions undermining confidence.
"Here in Berlin, I am calling for a jolt to Europe. We cannot continue as before," he told an audience at the Konrad Adenauer Foundation think tank, which has close ties to Merkel's conservatives.
Fillon said this would require "defining our priorities", including in economic and security policy, and reasserting shared values.
"In the current situation, where our Europe is threatened with disappearance from the international stage, it is our responsibility to take decisions," he said.
Delivering a passionate defence of the Franco-German partnership, Fillon said citizens must also live up to their duties to sustain European unity in turbulent times, even as Brexit threatens to undermine the cohesion of the EU.
"Instead of asking what Europe can do for us, we should ask ourselves what we can do for it," borrowing a phrase from US President John F. Kennedy's 1961 inaugural address.
But he offered tough talk on two of the most highly charged issues of the campaign: Islamist extremism and immigration.
"If borders are not protected by our European partners, and in the context of the war against Islamic totalitarianism, France will re-establish real checks at its borders," he pledged.
Earlier, the former French prime minister held separate closed-doors talks with Merkel, Defence Minister Ursula von der Leyen and Finance Minister Wolfgang Schaeuble.
Polls currently show far-right candidate Marine Le Pen qualifying for the second round of the French presidential election in May where she is forecast to face -- and lose to -- Fillon.
Le Pen, who says children of illegal immigrants should be refused public schooling, is an outspoken critic of Merkel's liberal refugee policy that led 890,000 people from mostly war-torn countries to seek refuge in Germany in 2015 alone.