"I'll do what is needed to keep the United Kingdom in Europe, but on condition that Europe can still move forward," Hollande told French radio as a key Brussels summit was set to go on late into the evening.
But with Prime Minister David Cameron seeking a package of reforms ahead of a referendum on British membership of the bloc, Hollande said Britain could not have "special rules" for the City of London, its financial sector.
Cameron has said that unless he gets a satisfactory deal, he will not campaign for Britain to stay in the 28-nation European Union in a referendum that he is expected to hold as early as June.
The British premier faces opposition from eastern European countries such as Poland over his plans to limit access to benefits for migrants.
He also faces trouble from France and Belgium over his bid to make clear that Britain is not committed to ever-closer union.