Rep. Jesse Jackson Jr. will announce Wednesday that he is resigning from Congress, a source close to Jackson said.
Jackson, who has been treated for what he described last month as "several serious health issues," is the subject of several investigations.
Voters in his South Side Chicago district re-elected Jackson, 47, for a 10th two-year term this month, despite his legal and health troubles.
Jackson, the son of civil rights leader the Rev. Jesse Jackson, is the subject of investigations by the FBI and House Ethics Committee.
His House colleagues are looking into allegations that, in 2008, he or one of his associates offered to raise money for then-Illinois Gov. Rod Blagojevich in exchange for Jackson being appointed to the Senate seat vacated by Barack Obama.
Jackson has been out of the public eye and absent from Capitol Hill for much of the past year, including while he was being treated at the Mayo Clinic as recently as last month.
He made no campaign appearances, relying instead on a recorded automated call made to constituents in October in which Jackson said, "the good news is my health is improving, but my doctors tell me the road to recovery is a long one."
"Like many human beings, a series of events came together in my life at the same time and they've been difficult to sort through," he said in the call, which his office provided to CNN. "I am human, I am doing my best, and I am trying to sort through them all."
In early July, the congressman's office announced he was "receiving intensive medical treatment at a residential treatment facility for a mood disorder." A few weeks later, his office said he was undergoing an "extensive inpatient evaluation for depression and gastrointestinal issues" at the Mayo Clinic.