According to Deadline, Howarth will play investigative journalist Mason Bridge who is looking into Dr. Wells, the mentor of the series title character.
The Flash co-stars Jesse L. Martin, who is the godfather of Howarth's son, Julian. Martin and Howarth met in the early 1990s while working on Guiding Light. They later worked together on One Life to Live.
There's no word yet on when Howarth will first air or the duration of the gig.
"We are thrilled for Roger and this opportunity," GH executive producer Frank Valentini said in a statement. "Fans can rest assure he is not off the show, as the timing for this role worked out so that he can shoot during our current GH hiatus.
This will not be the first time that Howarth will appear in primetime while on contract with GH. In June 2013, Howarth landed a recurring deal on Californication.
The Flash airs Tuesdays at 8pm ET/7pm CT on the CW.