They will battle in the first round of elections on Sunday
, standing on vastly different platforms from far-right to far-left.
But the candidates' initial reactions focused on the police who were targeted by a shooter on the Champs-Elysees, not politics.
Far-right presidential candidate Marine Le Pen, one of the front-runners, tweeted: "My emotions and solidarity for the police, once again targeted."
Conservative French presidential hopeful Francois Fillon tweeted: "Paying homage to police who give their lives to protect ours."
Leftist candidate Jean-Luc Melenchon, who's been rising rapidly in the polls, wrote on Twitter: "My thoughts are with the policemen dead and injured and their families. Terrorist acts will never remain unpunished. Accomplices not forgotten."
And Emmanuel Macron, a centrist who had to form his own party to get a nomination but has since found a great deal of support, also backed the police.
"I pledge all of my solidarity with regard to our law enforcement forces. My thoughts are with the family of the victim," he tweeted.
Socialist candidate Benoit Hamon added his condolences, again highlighting the work of the security forces.
"My thoughts go with the policeman who was killed, to his colleagues, who are hurt. Complete support to law enforcement against terrorism," he said on Twitter.
Voters in France go to the polls on Sunday in the first round of the presidential elections. The top two vote-getters from a crowded field will go head-to-head in the second round on May 7.