House Minority Leader Nancy Pelosi, D-Calif., met with Jackson and his father today.
"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."
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.
ABC's John Santucci, Amy Walter, John Parkinson, Jason Ryan and Sarah Parnass contributed to this report.