TV Guide reports that the singer will play a woman who is separating from her husband.
The man Rimes's character is married to is a celebrity who is on trial for a hit-and-run.
Drop Dead Diva's executive producer Josh Berman said: "When we created this role, we specifically had LeAnn in mind. Her character is complex, brilliant and just when you think you know her, she'll throw in a twist you won't see coming."
New Dancing With The Stars contestant Wendy Williams will also guest star in the show. Meanwhile, Paula Abdul will make another appearance to give relationship advice to Jane (Brooke Elliott).
Drop Dead Diva will return this summer on Lifetime.