“Signing is good, ratifying is better,” Hollande quipped at the Élysée Palace ceremony, flanked by environment minister Ségolène Royal, foreign minister Jean-Marc Ayrault and other top officials.
He noted that the deal will not come into force unless at least 55 countries responsible for at least 55% of global greenhouse gas emissions ratify it.
So far 17 states – mainly small island and low-lying coastal countries that are especially vulnerable to the sea-level rise – have ratified the deal.
Hollande called on other European countries to follow France’s lead by the end of the year.
At the December COP21 gathering in Paris, 195 governments reached the historic agreement setting a target of limiting global warming to “well below” 2C compared with pre-industrial levels.
The French hosts of the meeting, held just weeks after the devastating November terror attacks on Paris, were showered with praise for its success, notably Hollande and then foreign minister Laurent Fabius.
The 32-page deal also calls on rich nations to muster at least $100bn (£70bn) a year in climate aid from 2020. Just how that will happen has yet to be worked out.
COP21 is the acronym for the 21st conference of parties to the UN Framework Convention on Climate Change (UNFCCC), the arena set up under the 1992 Earth Summit in Rio.