For those of you who don't know, Shipp played Barry Allen in the 1990 version of The Flash. Here is the statement :
Given his history with The Flash, Andrew [Kreisberg], Geoff [Johns] and I could only think of one person we wanted to play Barry's father and that was John Wesley Shipp," Flash executive producer Greg Berlanti said in a statement. "He gives a fantastic and emotional performance in the pilot and we are looking forward to his presence in many more episodes. Also, personally, it was just wonderful to work with him again since my days at Dawson's Creek. He's a great actor and a great guy.