Oregon Gov. John Kitzhaber announced Friday he would resign amid a mounting ethics scandal involving him and his fiancée -- even as he remained defiant, lashing out at the media and former allies. 

“I am announcing today that I will resign as governor of the state of Oregon,” Kitzhaber said in a written statement. 

The resignation, which will go into effect Wednesday, marks the end of one of the longest political careers in Oregon’s history. Last month, Kitzhaber was sworn in to serve an unprecedented fourth term as the state's governor. 

But the rapidly accelerating political pressure to resign, coupled with various investigations and intense media scrutiny, proved too much to withstand. The governor took a few parting shots at his critics in his statement on Friday, calling it "deeply troubling to me to realize that we have come to a place in the history of this great state of ours where a person can be charged, tried, convicted and sentenced by the media with no due process and no independent verification of the allegations involved."

He added: "But even more troubling -- and on a very personal level as someone who has given 35 years of public service to Oregon -- is that so many of my former allies in common cause have been willing to simply accept this judgment at its face value. It is something that is hard for me to comprehend -- something we might expect in Washington, D.C. but surely not in Oregon.” 

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Two days ago, Kitzhaber had said he had no intention of resigning, despite growing pressure from almost every single top lawmaker in Oregon, including his friends and one-time political allies.

“It is not in my nature to walk away from a job I have undertaken — it is to stand and fight for the cause,” he wrote in his lengthy statement Friday. Kitzhaber maintained he has broken no laws but understands he has “become a liability to the very institutions and policies to which I have dedicated my career and, indeed, my entire adult life.”

The decision capped a wild week in which Kitzhaber seemed poised to step down, then changed his mind, but ultimately bowed to calls from legislative leaders that he quit the state's top job. 

Secretary of State Kate Brown, a Democrat like Kitzhaber, was expected to assume the office and become the first openly bisexual governor in the country. Unlike most states, Oregon does not have a lieutenant governor, and the state Constitution puts the secretary of state next in line.

Kitzhaber has been embroiled in a series of controversies involving his fiancee Cylvia Hayes. The pressure mounted earlier this week. First, the state attorney general, who is also a Democrat, confirmed she had opened a criminal investigation. Then, the governor summoned the secretary of state from Washington, D.C., to meet with him, only to inform her he would not resign -- the governor, according to the Associated Press, briefly decided to resign, and then changed his mind while the secretary of state was en route to Oregon.

Then on Thursday, the two top-ranking Democrats in the legislature called on Kitzhaber to step down.

Kitzhaber had hired prominent Portland criminal defense attorney Janet Hoffman amid the drama. Investigations, including another reportedly launched by the FBI, center around Hayes, who has pocketed more than $200,000 as a consultant during the same time she was the acting first lady as well as an adviser to the governor.

On Thursday, Oregon’s Senate President Peter Courtney said he and House Speaker Tina Kotek both asked Kitzhaber to step down.

“I finally said, ‘This has got to stop,’” Courtney said after he and Kotek met with the governor. “I don’t know what else to do right now. It seems to be escalating. It seems to be getting worse and worse.”

The spiral marks a remarkable fall for a politician in his fourth term as governor, and who has been an elected leader in Oregon for 37 years.

Fox News' Dan Springer and The Associated Press contributed to this report.