The couple got engaged in Fiji on the dating competition series in August 2010.
Chris Harrison will serve as host of "The Bachelorette: Ashley and J.P.'s Wedding."
The program will "let viewers in on all the exciting festivities -- from her dress fitting for her dazzling custom-made gown to Ashley and J.P. planning the big day with their wedding planner," ABC said in a news release. "Then it's on to their bachelor and bachelorette parties, and the next stage of their romantic journey with a beautiful wedding ceremony in the perfect location. Past 'Bachelor' and 'Bachelorette' couples, stars and participants [to be announced at a later date] will be on the guest list to help the couple celebrate, along with their families and friends."