Rep. Jesse Jackson Jr. (D-Ill.) submitted a letter announcing his resignation from Congress to Speaker John Boehner (R-Ohio) on Wednesday, according to a Boehner aide.
"For seventeen years I have given 100 percent of my time, energy, and life to public service," Jackson wrote.
"However, over the past several months, as my health has deteriorated, my ability to serve the constituents of my district has continued to diminish. Against the recommendations of my doctors, I had hoped and tried to return to Washington and continue working on the issues that matter most of the people of the Second District. I know now that will not be possible."
Jackson's resignation comes amid reports that he is being investigated by the Justice Department for allegedly misusing campaign donations to redecorate his home.
Reports earlier this month said Jackson was negotiating a plea deal with federal investigators that would require him to resign from Congress, citing health reasons, and repay the campaign funds.
Jackson's office has not commented on the reported plea talks.
Jackson wrote that he has "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."
Jackson has also been previously accused of planning to raise campaign funds for then-Illinois Gov. Rod Blagojevich in exchange for being appointed to President Obama's vacated Senate seat.
Late Tuesday, reports said that the Illinois lawmaker's office had scheduled a conference call Wednesday morning to address his staff about his future plans. Jackson's office, however, canceled the call.
On Wednesday, Jackson's office at the U.S. Capitol was locked, and no one answered a reporter's knock.
Illinois Gov. Pat Quinn said in a tweet Wednesday afternoon that he will announce a schedule for a special election to fill Jackson's vacated congressional seat within the next five days.
House Minority Leader Nancy Pelosi (D-Calif.) said Jackson's time in Congress was marked by his "eloquent advocacy for his constituents."
"It is with great sadness that we learned of Congressman Jackson’s decision to submit his resignation. His service in Congress was marked by his eloquent advocacy for his constituents’ views and interests," Pelosi said in a statement. "Through his public statements and his writings, he presented a fresh perspective on how we work together to form a more perfect union.
"As he works to address his health, our thoughts and prayers are with him, his wife Sandi, his children as well as his parents. We are grateful to him and his family for their longstanding record of public service to our country."
Pelosi spoke with Jackson and his father, the Rev. Jesse Jackson, early Wednesday afternoon.
Jackson easily won reelection in his heavily Democratic district. He released a robocall asking his supporters to stand with him as he dealt with his health issues but did not take part in any other campaign activities.
Jackson has faced pressure in recent days from many Democrats, including Sen. Dick Durbin (D-Ill.) and Chicago Mayor Rahm Emanuel, to speak to his constituents and assure them that he would be able to continue serving effectively in Congress.
Both Obama and Emanuel endorsed Jackson in his primary against former Rep. Debbie Halvorson (D-Ill.) earlier this year.
— Jeremy Herb contributed to this report.
— Posted at 1:35 p.m. and last updated at 5:13 p.m.
Read the letter below: