Modine, who was recently on The WB's "Bedford Diaries," will play Sullivan Goff, a mysterious land developer for Majestic, the new Christian church development being built near Agrestic, Zap2it.com reported Saturday.
Modine's character reportedly will have business and personal interaction with Mary-Louise Parker's Nancy and Elizabeth Perkins' Celia.
Modine is set to appear in at least 10 of the 15 episodes in the Showtime comedy's third season.
Also guest starring in the third season will be Zooey Deschanel as Justin Kirk's character's slightly deranged ex-girlfriend, Cat, as well as Carrie Fisher, who will play Arlene, Celia's divorce attorney.
"Weeds" has been nominated for four Golden Globe awards, including best television comedy.