Marcil will reprise her role as fan favorite Brenda Barrett, for which she won a Daytime Emmy in 2003.
"True to form, Brenda arrives in Port Charles with a secret that will impact Sonny, Jax and Jason," ABC president Brian Frons said in a statement. "General Hospital has always been dedicated to the strong history of our characters. Fans and viewers alike will be thrilled with her storyline and will agree that her return was worth waiting for."
During Marcil's first episode back — airing August 11 — Brenda finds herself in trouble and in possession of an explosive secret that could wreak havoc on the lives of her loved ones.