St. Clair County Circuit Court Judge Michael O'Malley will retire July 31 to enter private practice, four years before his current term expires.
O'Malley said he would open an office in St. Clair County for Carey & Danis. The firm Carey, Danis & Lowe is based in St. Louis and also has an office in Godfrey.
The firm promotes "aiding victims of corporate abuse, neglect and greed" on its website.
O'Malley said he assumes the bulk of the work he will undertake will be class actions in federal and state court. He said he would pursue cases against pharmaceutical companies.
His decision to retire before his term ends in December 2014 was pension-related, he said.
"I vested sooner than I thought," he said.
O'Malley, a Democrat, has served as judge for 25 years.
Illinois Supreme Court Justice Lloyd Karmeier, a Republican, will make a recommendation to the full court for a replacement to serve the remainder of O'Malley's six-year term.
In the 2008 general election, O'Malley was retained with 72 percent of the vote.
Judicial retirements typically do not occur so soon into a term.
O'Malley said he put his family's desires first in making his decision.