Wickersham, best known for her roles in The Sopranos and Gossip Girl, will play Eleanor "Ellie" Bishop, "a mysterious mixture of analytic brilliance, fierce determination and idealism who specializes in international threat assessment and global preparation."
The actress will serve as a replacement for Cote de Pablo, who departed from the show after playing Ziva David for eight seasons.
Pablo told TV Guide she left "under my own terms" over "personal reasons." CBS CEO Les Moonves said the network offered her "a lot of money" to stay.
NCIS, which airs Tuesdays, is an American television police procedural currently in its 11th season.