Jackson, who just won reelection in his Chicago district, has been dogged by controversy. He's been on medical leave from Congress for months and he is now under investigation for allegedly misusing campaign funds.
Update at 3:02 p.m. ET. Jackson Resigns:
After much controversy over an extended medical leave and facing an ethics investigation, Rep. Jesse Jackson Jr., a Democrat from Chicago, resigned from Congress today.
In a letter to House Speaker John Boehner, Jackson said he resigning effective immediately so he can "focus on restoring my health."
"During this journey I have made my share of mistakes. I am aware of the ongoing federal investigation into my activities and I am doing my best to address the situation responsibly, cooperate with investigators and accept responsibility for my mistakes, for they are my mistakes and mine alone," Jackson said in the letter. "None of us is immune from our share of shortcomings or human frailties and I pray that I will be remembered for what I did right."
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The Tribune attributes the news to Jackson's brother Jonathan Jackson, while the Sun-Times attributes it to "a source close to Jackson."
The Associated Press reports that aides to House Speaker John Boehner said his office had received a letter from Jackson telling Boehner of his intention to resign.
Jackson, who just won reelection in his Chicago district, has been dogged by controversy. First he took months of medical leave without giving a prompt explanation as to why and then federal authorities announced they were investigating whether Jackson misused campaign dollars to decorate his Washington, D.C. home.
Jackson, his doctors finally revealed, was suffering from bipolar II, "a treatable condition that affects parts of the brain controlling emotion, thought and drive and is most likely caused by a complex set of genetic and environmental factors."
The Tribune adds:
"Although he did not wage a campaign, Jackson won re-election on Nov. 6 to another two-year term in the House by defeating a Republican and independent challenger. Under Illinois law, Gov. Pat Quinn, a fellow Democrat, would call a special election to fill Jackson's 2nd District congressional seat, which extends from Chicago's South Side to Kankakee.
"He is the son of the Rev. Jesse Jackson, the civil rights leader, and the husband of Chicago Ald. Sandi Jackson, 7th."
We'll have more on this story as it unfolds.
Update at 2:50 p.m. ET. 'Remembered For What I Did Right':
NBC News' Luke Russert has obtained Jackson Jr.'s resignation letter. He has tweeted excerpts.
"None of us are immune from our share of shortcomings and human frailties. I pray I'll be remembered for what I did right," Jackson said. "During this journey I've made my fair share of mistakes, I'm aware of an ongoing investigation into my activities... I'm doing my best to address the situation responsibly, cooperate with investigators and accept responsibility for my mistakes."