"It's 2015. It's nearly a hundred years since women won the right to vote and yet men outnumber women in parliament by two to one," said WE leader Sophie Walker.
"So we have concluded that -- as a temporary measure -- quotas are necessary," she added, calling for political parties to field women in two-thirds of constituencies.
The party aims to have parity in parliament by 2025.
It was set up in March 2015 by television personality Sandi Toksvig and Catherine Mayer and has since grown to 45,000 members and supporters across the country.
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WE also demanded action to reduce the pay gap between men and women.
"Last year, men earned 516 billion pounds, while women earned just 271 billion pounds, that's a difference of 245 pounds billion pounds (334 million euros, USD 378 million)," said Walker.
"Why? Because millions of women are being paid less than their male colleagues and they are leaving work because they can't afford childcare," she added.
The party is also calling for government-funded childcare for all children from the end of paid parental leave at nine months.
On average, British women working full-time earn 9.5 percent less than men, according to a government study, while only 25 percent of judges and 23 percent of FTSE-100 company board members are women.