The Will & Grace star has appeared in previous seasons of the show as Tammy 2, the ex-wife of Parks director Ron Swanson - played by her real-life husband Nick Offerman.
Mullally will reprise the role in the ninth episode of the current season, according to TVGuide.
Titled Ron and Diane, the episode will focus on Ron and his new love interest Diane (Lucy Lawless).
Mullally's character will reportedly cause trouble for the new pair as she tries to win Ron back.
Parks and Recreation airs on Thursdays at 9.30/8.30c on NBC.