Underwood debuted in May 2006 as the edgy, bad girl, who was subsequently adopted by Dorian Lord. One Life to Live was the actress' first contract role as an actor.
"Thank you all so much for your kind words, I will miss you guys more than you know," Underwood posted on her Twitter page. "It has truly been a pleasure."
An ABC spokesperson confirms that Underwood will be departing the show, and states that the exit was storyline-dictated.
Underwood will last air on April 12.