The number of artworks by women in the revamped Tate Modern has more than doubled as part of its £260 million redesign.
Half of solo rooms are now dedicated to female artists, while the number of works by women make up 36%.
At an event to mark the reopening, London Mayor Sadiq Khan praised the gallery for "leading the world".
Speaking in the Turbine Hall he said: "Pioneering new approaches, seeing the potential for change, thinking big, putting people at the heart of what they do: that's what has made Tate Modern the success it is, and I want to apply that kind of thinking to how we approach culture in London.
"A modern museum for the 21st century. And you know what? There are a record number of female artists. Do you know what else? Half of the solo displays are female artists.
"The Tate Modern is once again leading the world. And that is exactly what we need."
The contemporary art gallery is reopening to the public on Friday with a new wing, the Switch House, designed by architects Herzog & de Meuron. This increases the size of the gallery by 60%.
The 10-storey building is topped by a public viewing level offering a 360-degree panoramic view of London.
Seventy-five percent of the artwork on display has been acquired since the gallery opened in 2000, with the Tate Modern now featuring artists from more than 50 different countries.
Tate Modern director Frances Morris said it had been an effort made to "acknowledge the contribution of women artists".
She said: "Fifty percent of the solo rooms in the Boiler House are by women artists, many of whom will be unfamiliar to people, but they're great works."
They include Polish artist Magdalena Abakanowicz, South African sculptor Jane Alexander and French-American artist Louise Bourgeois.
Frances said: "You can rewrite history, but you can't reinvent it. It wasn't a level playing field, so we are finding great contributions of women but of course there is an imbalance in the history.
"But the nice thing in the discoveries we've made, and installing the work, is how strong and interesting and experimental and original so much of the work feels."
She added: "It really is a new Tate Modern."
Director of the Tate Sir Nicholas Serota said he is excited to reveal a much more diverse collection.
"I think the most exciting thing is the fact that we're showing work from across the world, not just from north-west Europe and North America," he said.
"That's the big change since 2000. We're showing many more women. If you look at the single artist rooms, half of them are women and we're showing some spectacular new acquisitions and we're giving people the opportunity to have a new view of London."
He added: "London is a cosmopolitan city, it's a city that has always looked out to the rest of the world and I think that we all recognise that over the last 50 years, important work has been made in Latin America, Asia, North Africa, the Middle East, and there needs to be a small number of museums in the world that show that."
The museum has now reached a "balance", he said.