In the film, McGregor will play Bill Fordham, the estranged husband of Barbara (Roberts) and son-in-law of cancer-stricken drug addict Violet Weston (Streep).
Other actors reported to be in the cast include: Olivier Award winner Benedict Cumberbatch (Frankenstein, "Sherlock") as "Little" Charles Aiken, the son of Mattie Fae Aiken; Tony nominee Margo Martindale (Cat on a Hot Tin Roof) as Mattie Fae; Oscar winner Chris Cooper ("Adaptation") as Mattie Fae's husband, Charlie Aiken; Dermot Mulroney ("My Best Friend's Wedding") as Steve Heidebrecht; Oscar nominee Juliette Lewis as Karen Weston, who is engaged to Steve; Oscar nominee Abigail Breslin (The Miracle Worker, "Little Miss Sunshine") as 14-year-old Jean Fordham, the rebellious, pot-smoking daughter of Barbara (Roberts).
Sam Shepard (Heartless) is reportedly in talks to play the gone-missing patriarch Beverly Weston. Beverly's disappearance at the top of Letts' three-hour Pulitzer Prize-honored, Tony Award-winning play sets the story into motion.
The darkly comic August drama is a large ensemble piece (with three sisters at its core) set in a rambling house in Oklahoma. Letts also penned the screenplay. Wells (TV's "E.R." and "Shameless") will helm the film adaptation.
The Weinstein Company film is a Jean Doumanian / Smokehouse production produced by George Clooney and Grant Heslov, Jean Doumanian and Steve Traxler. Claire Rudnick Polstein is the executive producer.
Jean Doumanian Productions has produced the Tony Award-winning productions of August: Osage County, The Book of Mormon and Death of a Salesman.
Here's how TWC characterizes the picture: It "tells the dark, hilarious and deeply touching story of the strong-willed women of the Weston family, whose lives have diverged until a family crisis brings them back to the Midwest house they grew up in, and to the dysfunctional woman who raised them. Letts' play made its Broadway debut in December 2007 after premiering at Chicago's legendary Steppenwolf Theatre earlier that year. It continued with a successful international run."