Despite claims to the contrary, the character will not be on the show.
By Robert Marrujo:: Fox's Gotham has a rocky track record with fans, playing fast and loose with Batman mythology sometimes for good and other times for ill. The promise of beloved character Harley Quinn to the world of the show was something that many fans we optimistic about, but sadly her arrival has been dashed. Showrunner John Stephens had this to say to CBR before tonight's launch of Season 4:
“It’s not going to happen. Let’s put it out there. The discussions we’ve been having is – Look, we know Harley Quinn is never going to be on our show.”
Sadly, the attitude towards Dr. Quinzel's inclusion was much more on the positive end of the spectrum, even as recently as last season. The frontrunner for who would transform into Harley has long been character Barbara Kean. It seems that fans of Gotham will have to simply be content with her being a "Harley-esque" character, instead.
Gotham Season 4 debuts tonight on Fox.