Madigan, 46, is in her third term as attorney general. Earlier Monday, when asked if she would run for governor, she said she had not made up her mind. Illinois Gov. Pat Quinn was also at the ribbon cutting for the Navistar Company's new testing and development center, and the two Democrats barely spoke.
"When I make a decision you'll all find out about that," Madigan said Monday morning. "You'll find out when I do make one." Madigan, who has raised millions of dollars but remained coy about her plans, said she had contemplated a run out of frustration about the state's lack of progress on key issues. But she said it wasn't feasible while her father, Michael Madigan - arguably the most powerful politician in the state - remained speaker, a position he's held for 28 of his 42 years in the House.
"I feel strongly that the state would not be well served by having a Governor and Speaker of the House from the same family and have never planned to run for Governor if that would be the case," she said in a statement. "With Speaker Madigan planning to continue in office, I will not run for Governor."
For months, Lisa Madigan gave no hint about her plans, even brushing off reporters inquiring about her future at an event earlier Monday. Hours later, she announced in an emailed statement that she will seek re-election and that she enjoys her current job.
Her decision upends the emerging gubernatorial campaign, leaving Quinn with a likely Democratic primary challenge only from former White House chief of staff Bill Daley, the brother and son of two longtime Chicago mayors who has formed an exploratory committee.
Given her experience, backing and name recognition across the state through her job as the state's top attorney, Madigan was widely seen as having a strong chance at winning. Quinn faces increasing scrutiny about the effectiveness of his leadership as the state struggles with a nearly $100 billion pension funding shortfall and other issues.
Political experts offered mixed views on how her decision will affect Quinn's chances for re-election.
"It's a big help to Quinn," said political analyst Don Rose. "He'll be a leg up downstate ... and the Daley name may not be very popular downstate."
But others said it could hurt Quinn, if it allows his opposition to coalesce around Daley in a one-on-one primary face-off.
"In a three-way race, Daley and Madigan would be splitting the anti-Quinn vote," said Kent Redfield, who teaches politics at the University of Illinois at Springfield.
The governor's focus on Chicago and gun control in the recent debate over a new law allowing concealed carry of weapons fueled talk of downstate Democrats floating their own candidate, though any Democrat from outside Chicago faces disadvantages in fundraising, media exposure and name recognition.
Madigan's announcement came the day a fourth Republican candidate, state Sen. Kirk Dillard, made his bid official for 2014. State Treasurer Dan Rutherford, venture capitalist Bruce Rauner and state Sen. Bill Brady have already announced that they're seeking the GOP nomination in March next year.
Quinn's campaign didn't immediately have a comment Monday as the governor made stops around the state to talk about jobs. While he hasn't spoken in detail about his campaign plans for next year, he has said his focus is on doing his job but that he is ready for any challenger.
In a statement, Daley spokesman Pete Giangreco said Madigan's decision leaves voters with a "clear choice between a proven leader who gets things done and a governor who can't seem to get anything done."
Madigan has become one of the state's more popular officeholders in her three terms as attorney general, and easily won her last two elections. In the past year she raised her profile on a national stage, working with federal officials on consumer advocacy issues including mortgage practices.
Her ballooning campaign fund had stirred talk about her intentions - she raised $830,000 in the first three months of 2013 and has $4.3 million on hand, almost three times more than what Quinn reported April 1.
At the same time, the possibility of her candidacy also raised questions about her father and whether he would step down if she ran for governor.
Some political experts said he would have to step aside if she ran, if only to avoid the appearance of impropriety, while others said it shouldn't be a problem since Lisa Madigan already withstood similar questioning after winning statewide office while her father remains speaker. Madigan became the state's first woman attorney general in 2002, after serving four years in the Illinois Senate.
"I considered running for governor because of the need for effective management from that office and the frustration so many of us feel about the current lack of progress on critical issues facing Illinois," she said in her statement Monday.
Another factor in Madigan's decision might have been the recent spotlight on her father amid allegations of political influence in hiring at the Chicago area's Metra commuter rail service, according to political observers. In a memo Metra released last week, a former executive alleged that plans to oust him were tied to his refusal to accede to requests from Speaker Madigan for a pay raise for a Metra employee who made contributions benefiting the speaker and a job for another person.
Rose said the issue could have been a distraction for Lisa Madigan as she started a campaign for governor.
Madigan's decision is expected to affect other candidates for 2014 in the coming days.
Lt. Gov. Sheila Simon, who won't seek another term, has said that she was waiting to see what would happen before deciding what other statewide office to seek. She's unlikely to challenge Madigan, leaving comptroller and treasurer as other potential positions she might seek.
The Associated Press contributed to this report.