Video report by ITV News Deputy Political Editor Chris Ship
Angela Eagle has pledged to unite her party and the country as she formally announced her challenge to replace Jeremy Corbyn as Labour leader.
Describing herself as a "practical socialist", she said: "I'm not a Blairite, I'm not a Brownite and I'm not a Corbynista. I am my own woman."
Ms Eagle said the country faced "dark times" after leaving the European Union and said: "Jeremy Corbyn is unable to provide the leadership this huge task needs. I believe I can."
"I wouldn't do this if I didn't think I had something to offer to bring our party and our country back together," she told supporters in London.
She said the Brexit referendum result had left the nation "divided" and represented a "howl of pain" from neglected parts of the country.
"I'm not going to stand back and allow Britain to become a one-party Tory state," Ms Eagle said.
She said she accepted many in the country don't "believe" she and Labour can represent them, "But they will if I win this fight."
"I will unite. I will not divide," she said, adding: "I am ready to lead."
Ms Eagle's announcement looks set to trigger civil war within the party.
Mr Corbyn is bidding to fight to ensure that his name is on the ballot paper for a vote of the party's members, among whom he has strong support.
Ms Eagle's leadership bid comes after 172 Labour MPs indicated that they had no confidence in Mr Corbyn in a party vote.
The Labour leader was supported by only 40 Westminster colleagues but would be expected to garner large support from the party members.