"If the agreement is not legally binding, there will be no agreement ...," Hollande said in Malta, where he was attending the EU-Africa migration conference.
Kerry told Thursday's Financial Times that there was "definitively not going to be a treaty", as favoured by the European Union and many other countries.
While the conference will encourage a "significant amount of investment" in a low-carbon economy, "they're not going to be legally binding reduction targets like Kyoto," Kerry said, referring to the 1997 UN treaty that contained supposedly binding targets for cutting emissions.
"I know how difficult it is," Hollande said, in an apparent reference to Republican opposition to climate change action in the US. "But we must give the Paris agreement, if there is one, a binding character in the sense that the commitments that are made must be kept and respected."
French Foreign Affairs Minister Laurent Fabius, who was also in Valletta, earlier said Kerry's statement "could have been more fortunate".
It was "obvious" that some of the decisions must be legally binding, he added.
The Financial Times commented that EU officials accept that Barack Obama's administration wants a deal at the Paris conference but fears legal commitments because of opposition in the Republican-controlled Senate.