The show has been described as a dramatic reimagining of the 1960s sitcom about a family of monsters trying to fit into a middle-class human neighborhood.
"We want this show to be an American Harry Potter," writer-producer Bryan Fuller recently told EW.com. "To have that sense of a magical world that you get to go to with your family and find stories told in a fantastical way that are instantly relatable. It's an 'American Horror Story' that the whole family can watch."
British comedian Eddie Izzard was previously announced as the vampire character of Grandpa.
O'Connell, who will play Frankenstein's monster-inspired Herman, began his career as a child actor in the film "Stand By Me." His other movie credits include "Scream 2," "Kangaroo Jack," "Joe's Apartment" and "Jerry Maguire." He has also starred in the TV series "Sliders," "Crossing Jordan," "Las Vegas," "Eastwick" and "The Defenders."