A publicist for the couple announced the breakup Thursday in a statement that said the separation was "jointly decided" and that "primary focus and concern is for their son."
The pair met while appearing in "Rent" off-Broadway and married in 2003 after dating for seven years. They co-starred on Broadway in the show "Wild Party" in 2000 and on the TV show "Private Practice."
Their son, Walker, was born in 2009.
Menzel, 42, made her Broadway debut in "Rent" and won a Tony as Elphaba in "Wicked." Her films include "Enchanted," ''Rent" and "Ask the Dust." She also has launched a solo recording career and had a recurring role on TV in "Glee." She is currently starring in the Broadway-bound musical "If/Then."
Diggs, 42, who has been onstage in "Chicago" and is best known for his role as Winston Shakespeare in the hit 1998 romantic film "How Stella Got Her Groove Back," recently starred in "The Best Man Holiday."