Gummer's film credits include "Evening" and "Taking Woodstock."
She and Walker, who reportedly have been dating for about a year-and-a-half, co-starred in last year's Broadway production of "Les Liasions Dangereuses."
"He proposed two days ago," Usmagazine.com quoted Gummer as saying Monday. "He did it on one knee!"
Celebrity Couples of 2014 [PHOTOS]