Rep. Paul Ryan, R-Wis., formally announced his candidacy for speaker of the House of Representatives  Thursday after securing crucial endorsements from divided Republican factions.

"I never thought I'd be speaker. But I pledged to you that if I could be a unifying figure, then I would serve-I would go all in," the 2012 vice presidential nominee said in a letter addressed to members of the House Republican Conference, reported NBC News. "After talking with so many of you, and hearing your words of encouragement, I believe we are ready to move forward as a one, united team. And I am ready and eager to be our speaker."

Ryan was initially unwilling to mount a bid to succeed outgoing House Speaker John Boehner, who abruptly announced his plans to leave Congress by the end of October due in large part to stiff opposition from conservative members of the GOP conference.

Earlier this week, Ryan had a change of heart and said that he was open to replacing Boehner only if several conditions were met and he thought he could win the unified backing of his divided House colleagues.

One of Ryan's demands was that Congress change a procedural rule known as a "motion to vacate the chair," a parliamentary measure that members can use to try and oust a speaker and that had threatened Boehner's job, according to Fox News.

By Thursday afternoon, Ryan had received the required support from many conservative and moderate Republican groups and proceeded to announce his intentions, according to Reuters.

"We have an opportunity to turn the page, to start with a clean slate, and to rebuild what has been lost. We can make the House a more open and inclusive body-one where every member can contribute to the legislative process. We can rally House Republicans around a bold agenda that will tackle the country's problems head on. And we can show the country what a commonsense conservative agenda looks like," Ryan said in the letter.

Boehner told the House Republican Conference Wednesday that an internal vote for speaker will be held on Oct. 28, followed by a full House floor vote the following day. Candidates for the speakership will need roughly 218 votes to win the position, according to Fox News.