Dane County District Attorney Ismael Ozanne is running for attorney general.
In an emailed announcement Thursday, Ozanne pointed to his 13 years as a prosecutor and leadership experience in the state prison system as qualifications for the office.
"From the epidemic of heroin abuse to the increasing severity of domestic violence to Internet predators and human trafficking, we face significant law enforcement challenges," Ozanne said in a release. "It will take an experienced front-line prosecutor to meet those challenges."
Former Democratic Gov. Jim Doyle appointed Ozanne district attorney in 2010. He made headlines in 2011 after he unsuccessfully sued to stop Gov. Scott Walker's collective bargaining restrictions.
State Rep. Jon Richards, a Milwaukee Democrat, also declared his candidacy. So did Waukesha County District Attorney Brad Schimel, a Republican.
Matt Frank, who served in Doyle's cabinet, also are considering running.
Incumbent Attorney General J.B. Van Hollen announced in October he won't seek re-election.
A primary is will be held August 2014.