Preston ("Death Sentence," "Jerry Maguire") will make her first appearance on Monday, April 14. She'll play Meghan Doyle, a venture capitalist who decides to invest in Joe's (Jake Weber) solar power-based invention and become his business partner.
Her involvement with Joe ends up creating some friction in his marriage to Allison (Patricia Arquette).
"We're thrilled to have Kelly join us for the final episodes of season four," "Medium" creator Glenn Gordon Caron says. "For the role of Meghan Doyle ... we needed an actress who exuded both intelligence and sexuality. Someone who could stand toe-to-toe with Patricia and Jake, and credibly create chaos in a household and a marriage that is as strong as any on television."
Preston's recent film credits, in addition last year's "Death Sentence," include "Sky High" and "What a Girl Wants." She's also appeared in "Fat Actress," "For Love of the Game" and "Citizen Ruth."