Delta Wedding begins with the arrival of nine-year-old Laura McRaven at the Shellmound estate in Mississippi. An only child, she welcomes being with the large Fairchild family as their seventeen-year-old daughter Dabney is about to get married. At the same time, Laura is overwhelmed by their close-knit, large family headed by her uncle, Battle, and her aunt, Ellen, and their eight children.

The plot involves preparations for the coming wedding, in which Dabney will marry Troy Flavin, the plantation overseer who is twice her age and who comes from a family of lower status. Nonetheless, the family comes to accept him and embrace him. At the same time, Laura also becomes part of the family. At the beginning of the story, she makes a cake with her aunt, Ellen, symbolizing the way in which Laura is becoming enfolded into the family. Much of the book is dedicated to a detailed description of the way of life at Shellmound, portrayed in exquisite, slow-moving detail—meant to capture the timelessness of the Fairchild way of life in their slow-moving town.

At the same time, Uncle George, dedicated to his family, has fought with his wife, Robbie, because of a recent incident in which he tried to rescue his disabled niece, Maureen, from a train track and was nearly run over. At the last minute, the train stopped, but his wife feels that he puts his family before her. At the end, she is reconciled to the importance of the family. Laura also becomes part of the family, as she takes part in the wedding when a child who is supposed to be part of the wedding takes sick. She is both part of the family and part of the contingent that will eventually leave at the end of the wedding. At the end of the book, though Dabney is married, the family's life continues as Dabney settles at Marmion, a nearby house owned by the Fairfields, and Laura knows that she has a place with the family.