"Under the Mistletoe" is a Christmas pop[1] song written by Clarkson and Aben Eubanks, who produced the track with longtime collaborator Jesse Shatkin.[2] Clarkson invited Eldredge to record the song with her, saying that she was "impressed by his classic sound on his Christmas record so it was a perfect match." Eldredge immediately accepted the invitation, and remarked, "I was blown away by the soul and joy that it brought into my life the moment I heard it."[3]
Reviewing the track for Vulture, Rebecca Alter opined that the song may not be the best Clarkson Christmas song, but that it was "very good as well, going for that throwback, A Christmas Gift for You from Phil Spector sound that most Christmas songs have if they want to signal that they're "Christmas!"".[1] George Griffiths of the Official Charts Company opined that the track "packs enough pep to take you all the way through to the big day."[4]