TMJ4 reported that Milwaukee County Clerk George L. Christenson confirmed the development on Thursday, saying his resignation was received at 3:17 p.m. local time.
Clarke, a tough-on-crime conservative Democrat on paper, had become a favorite among conservatives with his provocative social media posts and his blind devotion to Donald Trump during his 2016 campaign.
Clarke did not immediately return an email seeking comment.
Milwaukee County Sheriff David Clarke at the National Rifle Association's annual meeting in Atlanta in April.
Conservative groups have called on Clarke to challenge Democratic U.S. Senator Tammy Baldwin in 2018, but he has rejected that suggestion. He later said he withdrew his name.
A lengthy inquest into the dehydration death of a Milwaukee County Jail inmate earlier this year raised troubling questions about how Clarke managed the jail - just as the White House was said to be considering him.
Clarke has been a vocal supporter of President Donald Trump and has been rumored as a nominee for secretary of the US Department of Homeland Security.
Clarke was one of the few African-Americans to speak at the Republican National Convention past year.
He rose to national prominence as a fierce critic of the Black Lives Matter movement with his charged conservative rhetoric.
He was hit by allegations in May that he plagiarized content in his master's thesis on homeland security, which he denied.
In January, after four inmate deaths in county jails, County Supervisor Supreme Moore Omokunde urged Clarke to resign.
While Clarke's misdirection of county law enforcement personnel to intimidate a civilian head-shaker has brought the heat down on him most recently, the episode hardly tops the list of the sheriff's scandals.