"There will be no agreement... If there is no firm commitment on finance" for developing nations, he said as ministers and diplomats from 57 countries met elsewhere in the French capital to discuss exactly this issue.
The November 30-December 11 UN conference is tasked with sealing a universal deal to roll back the threat of climate change.
But without an accord on finance, "countries will refuse, emerging economies... And they are right," the president told journalists.
The overarching goal is to limit average global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-Industrial Revolution levels -- the threshold at which scientists say we can still avoid worst-case-scenario climate effects.
More From This Section
Hollande addressed a press conference as foreign and environment ministers and senior officials concluded two days of talks on the finance question.
Funding is the key to help developing countries shift to greener energy, adapt to a climate-altered world and deal with the loss and damages they will suffer from rising seas, droughts, storms and other impacts.
At the end of the informal ministerial meeting, French Foreign Minister Laurent Fabius insisted the USD 100 billion commitment "must be respected."
In a bid to "give credibility to the process," he said, France and Peru, which hosted last year's climate conference, had asked the Organisation for Economic Cooperation and Development (OECD), a coordinating forum on economic matters, to provide clarity on how the figure will be fleshed out.
"This will naturally allow us to determine a trend, to see whether we are on track vis-a-vis the target of $100 billion in 2020, or if there are additional efforts to be made."
The ministerial talks were not part of official negotiations for the highly-anticipated agreement, but are meant to inject momentum into the troubled UN process.