Brady announced his resignation Tuesday in a letter to the state party's central committee.
Brady led the state GOP for nearly four years.
Most Republicans ABC7 talked to in Springfield said they are relieved Brady decided to resign now, and not in the midst of the 2014 campaign season, which could begin within the next couple months.
This is not all about politics. Brady has struggled with a family health issue for most of the past two years.
"My wife is ill. She's been battling cancer for two years," Brady said Tuesday. "I haven't made that public until today because my kids weren't fully informed."
After telling ABC7's Jason Knowles that concern for his family is the reason for his resignation, Brady acknowledged the final year of his chairmanship had caused deep divisions within the Illinois Republican party.
"It has become quite a distraction," said State Senate Minority Leader Christine Radogno. "I think it's good that we're going to be able to move beyond that."
Under Brady's leadership, in 2010, Republicans won Illinois' Open U.S. Senate seat, wrested most of the state's congressional seats away from Democrats and made gains in the state house and senate.
But, in 2012, Illinois Republicans lost more than what they gained two years earlier.
Then, Brady went public with his personal support for same-sex marriage, a move that bucked the state GOP platform, outraging the party's right wing.
"What's gone on the last four or five months, my position on marriage equality, I've lost support of a lot of members of the central committee," said Brady. "I understand that. It's probably better for the party and for me to move on."
"If I were the chairman of the party, and I disagreed with some part of the platform, I just wouldn't say anything about it," said Republican State Senator Jim Oberweis, who represents North Aurora. "I would support, in general, the party's platform."
As he refocuses on his personal law practice, and perhaps opening a public affairs firm, Brady holds fast to his views on marriage equality.
"The party platform, nationally and locally, is on the wrong side of history. And the bedrock principal of conservative beliefs is equality of treatment under the law for everybody. And, if government's going to get in the marriage business, you can't let certain people do it and certain groups not do it."
The Republican state central committee will meet no later than early June to choose Brady's replacement.
Brady says he hopes to see a woman or a minority in the position he held.
Carol Smith Donovan, the current Vice-Chairman will serve as interim Chairman until the Illinois Republican State Central Committee selects a permanent replacement. The State Central Committee elected Brady as Chairman immediately after previous Chairman's Andy McKenna's resignation at Republican Day at the Illinois State Fair in August of 2009.