Sorkin's project, tentatively titled "More as This Story Develops," centers on cable news anchor Will McCallister (Daniels) and the show's female executive producer, MacKenzie, to be played by Mortimer.
As previously reported, Pill, currently starring in The House of Blue Leaves, has signed on to play Maggie, an associate producer on the assignment desk, and Olivia Munn will play a "sexy financial analyst" on the same cable network as McCallister.
Waterston was nominated in 1994 for a Tony Award for his performance in Abe Lincoln in Illinois. He has also been seen on Broadway in A Walk in the Woods, Benefactors, Lunch Hour and Hamlet.
Pill was nominated in 2006 for a Tony Award for her performance in Lieutenant of Inishmore, and Daniels was nominated in 2009 for a Tony Award for his performance in God of Carnage.