Harriet Harman, the Constitutional Affairs minister, has confirmed she will stand for deputy leader of the Labour party when it becomes vacant.
The 56-year-old is the first woman to enter the race for the position.
Ms Harman, the MP for Camberwell and Peckham in south London, said there needed to be a woman involved in the government's decision-making process.
Tony Blair has said that he will stand down as the party's leader "within the next 12 months".
Northern Ireland Secretary Peter Hain has already announced a challenge for the deputy leadership, when a vacancy arises, while Labour backbencher and ex-Downing Street aide Jon Cruddas has said he is also considering a bid.
"Really there seemed no point in not actually being quite clear," Ms Harman told BBC Radio 4's PM programme.
"I'm going to fight a strong campaign," she added.
She said she would be "running for deputy leader in a situation where that person would be deputy prime minister".
This was a reference to Mr Cruddas' call for major reforms of Labour, including an end to the automatic awarding of the role of deputy prime minister to whoever was number two in the party.
She went on: "We've got to reflect the fact that whilst the party used to be an exclusively men-only activity, that has changed.
John Prescott has been Labour's deputy leader since 1994
"Women in the country regard themselves as equal and they expect to see a team of men and women making decisions."
She elaborated on this in a separate interview with BBC Radio Northampton, saying: "My first instinct is that I object to the notion that when there's a difficult and important job to be done, you look around for the best man for the job."
But "a balanced team in a House of Commons where there's women as well as men" would result in "more sensible decision-making than if you're just got a men-only show".
She also revealed she had spoken to the prime minister about "the time of his departure".
She said she had privately "given him the benefit of my view about when I think he should go" but would not elaborate while talking to the PM programme.
Last week Ms Harman called for colleagues to "shut up" after a series of bitter personal attacks from the likes of Charles Clarke, the former home secretary.
It had been a "very difficult week" and a "worrying moment" in the party's history, she said, but Labour was now "back on track".
Ms Harman was the social security secretary for a year after Labour swept to power in 1997 and returned to the front bench when she became Solicitor General in 2001.
After the next general election in 2005 she took up her present role but gave up some of her responsibilities a year later to avoid a conflict of interest.
This was because her husband, Jack Dromey, was the party's treasurer and an investigation into loans to Labour was under way at the time.