Network Fox made the announcement on Wednesday during the Television Critics Association press tour.
The episode will feature animated versions of Legend and Teigen being recruited by Marge for an education-based proposal. The husband and wife will be voicing themselves.
"Who else by John Legend could sing a song so emotionally powerful that it would make the people of Springfield do something smart?" Simpsons executive producer Matt Selman told Entertainment Weekly.
Fox also announced other celebrities guest stars coming to their block of animated comedies which include new sitcom Bless the Harts, Family Guy and Bob's Burgers.
Bryan Cranston, Niecy Nash, Kenny Loggins, Mike Judge, Hank Azaria, Danny Trejo, Judy Greer, Chris Parnell, Christopher Meloni, and Nat Faxon will be featured on Family Guy while Bless the Harts will feature Fortune Feimster, Holly Hunter, Mary Steenburgen and Drew Tarver.