(ABC News) -- Rep. Jesse Jackson Jr., the embattled Democrat from Illinois who has been on medical leave from Capitol Hill for months undergoing treatment for bipolar disorder, resigned from the House of Representatives Wednesday.
Aides to House Speaker John Boehner, R-Ohio, said they had received a letter of resignation from Jackson Jr.
The news was first reported by ABC News' Chicago station WLS and two Chicago newspapers.
Jackson has faced a slew of problems in recent months, most recently a probe by federal investigators into his finances. The federal probe was trying to get to the bottom of "suspicious activity" connected to Jackson's House seat and potentially inappropriate expenditures.
Jackson's problems began in June when the son of civil rights leader Jesse Jackson suddenly left Congress. His office said he was seeking treatment for "exhaustion."
Two weeks later, his office noted that his condition was "more serious" than initially thought.
Jackson, whose district includes a large portion of Chicago's South Side and southeast suburbs, then spent some time at a treatment facility in Arizona before later moving to the Mayo Clinic in Minnesota.
Finally, in August, the clinic said Jackson was being treated for bipolar disorder, "responding well" and "regaining his strength."
In early September, Jackson returned home to his family in the nation's capital. A source told ABC News that day that Jackson "sounded good." However, despite the Congressional summer recess ending a week later, Jackson did not return to work.
Jackson has missed 230 votes in the House this year. He last voted on June 8.
Despite all his troubles, Jackson still managed to win re-election in a landslide earlier this month. But now, he will leave Congress shrouded by personal problems and professional probes.
According to state law, Illinois Gov. Pat Quinn will declare Jackson's seat vacant once the congressman gives official notice of his resignation, and there will be a special election to fill the seat.
Reached by ABC News Wednesday, one of Jackson's colleagues, Rep. Danny Davis, D-Ill., said he was not surprised that Jackson had decided to leave Capitol Hill, noting that Jackson had cancelled a conference call with constituents set for Wednesday morning.
"I did get the feeling that, if you've got plans to say something this morning and then you don't, that would probably indicate that you were pretty close to something," Davis said.
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