Michael Pitt has been arrested on sexual abuse charges ... with authorities accusing him of sexually assaulting his then-girlfriend and later attacking her with several blunt objects.

According to the indictment, prosecutors say Pitt's charges stem from four domestic incidents that allegedly took place between April 2020 and August 2021.

Cops claim the alleged incidents occurred at the actors Bushwick home with his then-girlfriend ... where they say fondled ex on one occasion and then -- months later -- allegedly sexually assaulted and struck her with a wooden plank.

At a different time, prosecutors claim he attacked the alleged victim with a cinderblock.

According to law enforcement sources ... Pitt was arrested on Friday, May 2 at 9 PM for assault injury with a weapon sexually motivated, strangulation sexually motivated, sex abuse, and forcible compulsion. Pitt pled not guilty to all charges against him. He posted $100K bail and was released from custody.

Fans of "Boardwalk Empire" will recognize Pitt as Jimmy Darmody ... a main character in the first two seasons of the show. The character was killed off because Pitt was reportedly hard to work with.

Pitt also appeared in "Hannibal," "Hugo," "Hedwig and the Angry Inch," "Dawson's Creek," and "Seven Psychopaths."

Pitt's attorney Jason Goldman tells TMZ ... “Unfortunately, we live in a world where somebody like Mr. Pitt — an accomplished professional who would never so much as contemplate these crimes — can be arrested on the uncorroborated word of an unhinged individual."