The 41-year-old actor is a huge fan of the TV series and had asked screenwriter and personally asked director Ryan Murphy if there was any way he could be included, reported Variety.
"I wrote a letter to Ryan, asking if I could be in it. And he didn't respond," Harris said.
However, Ryan has now written back, saying he has already started work on a role for the former 'How I Met Your Mother' star into the show.
'American Horror Story: Freak Show' is the fourth series of the show, broadcast on the FX network. It will follow a fictional version of one of the remaining Freak Show businesses of the 50s, based in Florida, and its struggle to stay alive.
The series will include returning cast members Evan Peters, Emma Roberts, Gabourey Sidibe and Jessica Lange.