Known for her appearance on "Smash" last year and, of course, being Meryl Streep's daughter, Gummer will play the right-leaning Hallie Shea on Season 2 of the HBO drama.
Other upcoming guest starsinclude Rosemarie Dewitt and Patton Oswalt, who famously bashed the series on Twitter this summer.
In other casting news...
Seth Gabel is joining "Arrow." The actor will play Vertigo, a “scary and nightmarish” super-villain on the CW series. [TVLine]
Brandon T. Jackson is "Beverly Hills Cop"-bound. Jackson will appear as Axel Foley's (Eddie Murphy) son Aaron, a Beverly Hills police officer, in the CBS pilot. [THR]
Dean Winters is on his way back to "30 Rock." Liz Lemon's ex is back! Dennis Duffy, also known as The Beeper King, will make an appearance on the NBC series' final episode. [Vulture]
Billy Dee William is stopping by "Modern Family." The "Star Wars" alum will play himself in an upcoming episode of the ABC series' New Year's episode. [EW]