Rep. Jesse Jackson, Jr. (D-Ill.) waves on the U.S. Capitol steps in Washington in 2011. (YURI GRIPAS/REUTERS)

Rep. Jesse Jackson Jr. resigned from the House on Wednesday, acknowledging that he is under federal investigation of public corruption and ending what once was one of the most promising and vibrant political careers in Washington.

The Illinois Democrat, the son of legendary civil rights leader Jesse Jackson Sr., had been a star among a generation of black politicians, including President Obama, whose political success would ratify the gains of the civil rights movement.

Jackson’s resignation followed a sometimes bizarre unraveling of his congressional tenure, which included a six-month absence from office and multiple stints at the Mayo Clinic in Minnesota as he battled depression and bipolar disorder.

His last recorded vote was on June 8, and he was not seen in public after that. Weeks went by without any acknowledgment from his congressional staff about his absence, and press releases rolled out as if everything was fine.

Justice Department officials would not say whether the resignation was connected to developments in the investigation or comment on the inquiry, except to say that it is ongoing.

In his resignation announcement, however, Jackson suggested the possibility of a deal:

“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 the investigators, and accept responsibility for my mistakes, for they are my mistakes and mine alone.”

Barely two weeks after easily winning a ninth full term for which he never publicly campaigned, Jackson’s official departure marks the end of a four-year free-fall in which the once-promising politician’s personal, legal, political and medical aspects of his life ended up in ruin.

“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,” Jackson, 47, wrote in an unusually personal two-page letter of resignation. He submitted it to the office of House Speaker John A. Boehner (R-Ohio) after telling high-level Democratic officials in Chicago and the state capital of his plans, congressional and Chicago officials said.

Elected to succeed a scandal-ridden lawmaker 17 years ago, Jackson had ambitions far beyond Chicago’s South Side-based 2nd Congressional District. Many viewed him as the heir that could fulfill the political aspirations of his father, whose presidential runs in the 1980s were considered the first credible campaigns by an African American for national office. Raised mostly in the District, the younger Jackson attended St. Alban’s School before enrolling in North Carolina A&T, his father’s alma mater. He also holds a master’s degree from the Chicago Theological Seminary and a law degree from the University of Illinois.

Four years ago, Jackson was a leading contender for an appointment to the Senate seat being vacated by Barack Obama, who had just been elected president.

But that moment of opportunity turned to doom when FBI agents arrested then-Gov. Rod Blagojevich (D) and charged him with trying to sell Obama’s Senate seat to the highest bidder.

Raghuveer Nayak, a fundraiser for Blagojevich and Jackson, told investigators that the congressman instructed him to raise as much as $6 million for the then-governor’s campaign.

Blagojevich, now in federal prison in Colorado, denied that his efforts were anything more than normal political fundraising, but the FBI and the House Ethics Committee have looked into Jackson’s bid to win the appointment. Blagojevich’s brother testified at trial that members of the city’s Indian American community offered $6 million in contributions if Jackson were appointed to the seat.

Jackson was never charged in connection to the Senate seat, but the U.S. attorney for the District of Columbia has been investigating allegations that Jackson improperly used thousands of dollars in his campaign fund for personal expenditures.

Justice officials declined to comment Wednesday.

As the investigations unfolded, Jackson’s family life crumbled. An affair he had with a Washington nightclub hostess became public, something he called “a private and personal matter between me and my wife.”

In late June Jackson’s office announced that the congressman was suffering from exhaustion, and in July it said he was being treated in the Mayo Clinic for depression. By mid-August, the clinic issued a statement saying he had bipolar disorder.

Despite his months-long absence from the District, Jackson won reelection on Nov. 6 with 71 percent of the vote, and congressional insiders wondered whether he would return to the Capitol. Instead, Jackson announced Wednesday that his medical condition makes that impossible.

“The constituents of the Second District deserve a full-time legislator in Washington, something I cannot be for the foreseeable future,” he said. “My health issues and treatment regimen have become incompatible with service in the House.”

By law, Illinois Gov. Pat Quinn (D) will call a special election to replace Jackson within the next 115 days.

Among the names being mentioned for the safely Democratic seat are Jackson’s wife, Chicago Alderwoman Sandi Jackson (D), Cook County Chief Administrative Officer Robin Kelly (D), state Sen. Toi Hutchinson (D) and state Sen. Napoleon Harris (D), a former football player at Northwestern University and in the NFL.

Also being mentioned is former congressman Mel Reynolds (D), who resigned the seat after being convicted of charges related to child pornography and sexual misconduct with a 16-year-old campaign worker.

In that 1995 race to succeed Reynolds, Jackson signaled his ambition from the outset, hoping to accrue power over a long career. “The only way one grows into leadership in Congress is to get elected young enough that you become speaker of the House or chairman of the Ways and Means Committee,” he said.

By 2008, he wanted a bigger platform. He took an early role as a surrogate for then-Sen. Obama’s presidential campaign, viewing that candidacy as the emergence of his generation of black leaders taking over from his father’s generation. He picked public fights with his father, criticizing “Reverend Jackson” for his jabs at Obama.

Rather than lifting him into a bigger political role, Obama’s election set off the downward spiral that culminated in Wednesday’s resignation.

Jackson thanked his constituents for sticking by him during his troubles.

“I thank them for their patience, words of support and prayers during what has been, and what will continue to be, a very trying time for me and my family,” he wrote.

Aaron Blake and Ed O’Keefe contributed to this report.