Women across the globe marked the day with calls for greater political power.
"There are now 11 women heads of state or government, in countries on every continent. And three countries - Chile, Spain and Sweden - now have gender parity in government," Mr Annan told the Commission on the Status of Women.
He said this sends a clear message: "the world is ready for a woman as secretary-general of the United Nations".
Mr Annan will step down in December after 10 years at the helm of the world body.
He spoke shortly before a scheduled meeting with Latvian President Vaira Vike-Freiberga, the only female contender for his position.
Tens of thousands of women across the world rallied against inequality, sexual violence and discrimination to mark the annual day.
"Around the globe, women are making impressive gains," US Secretary of State Condoleezza Rice said in a statement.
However, she added, "In too many parts of the world women still struggle for basic liberties under governments that tolerate discrimination, systematic abuse, exploitation and violence against women".
Women's rights activists echoed the opinion of Mr Annan, pointing to the rise of Ellen Johnson Sirleaf of Liberia as Africa's first elected woman head of state, the unprecedented victory in Chile of President Michelle Bachelet and Germany's first-ever female chancellor, Angela Merkel.
"Women's role in society has now been set on a new path, on an irreversible path, where we can claim the leadership, we can seize the moment," Ms Sirleaf said during an event in Paris.
In Chile, Ms Bachelet's election represented a "cultural change" in which chauvinist habits were being left behind, outgoing president Richard Lagos said.
Ms Bachelet, 54, an agnostic paediatrician and single mother in a staunchly Catholic country, has named a cabinet with as many women as men.
Appeals for more gender balance in government came from far and wide, as the UN estimated that, worldwide, it will be 2025 before there is an average of 30 per cent of women in parliaments and 2040 before there is parity.
UN officials urged women to enlist as candidates in the Democratic Republic of Congo's first planned free elections in over 40 years.
In Lisbon, the Portuguese government said it would introduce a law requiring one-third of election candidates on party lists to be women.
Women around the world also called for more attention to violence against women in the developing world.
In Multan, Pakistan, 3,000 people, mainly women, attended a rally led by 33-year-old Mukhtaran Mai, who was gang-raped on the orders of a rural tribal council in 2002 as punishment for her brother's alleged affair with a woman from another tribe.
"I will continue my struggle to end the oppression of women," Mai told the crowd as it chanted "Give equal rights to women!" and "Treat women with respect!".
In Malaysia, the daughter of former prime minister Mahathir Mohamad sparked on outcry when she likened the status of Muslim women there to South African blacks under apartheid.