The Australian actress, who can currently be seen in BBC Four's The Slap, will play Sam in the espionage thriller.
Sam, who works for a private intelligence firm, is almost assassinated and suspects members of her team. When she returns to work, she is unsure who to trust.
George has also appeared in shows including Home & Away, Grey's Anatomy, Alias and In Treatment. She recently signed up for an American adaptation of Stephen King's Bag of Bones.
Nemesis will also star Adam Rayner as Aidan, Sam's colleague and love interest. Rayner's previous credits include Mistresses and the US drama HawthoRNe.
Nemesis, written by Strike Back scribe Frank Spotnitz, features a larger cast including Stephen Dillane, Morven Christie, Adewale Akinnuoye-Agbaje, Lex Shrapnel, Uriel Emil, Patrick Malahide, Stephen Campbell Moore and Oscar Kennedy.
Spotnitz promised that the series has "action on a cinematic scale, huge story twists and turns, and intriguing characters who are both emotionally and morally complex".
Meanwhile, BBC One's drama controller Ben Stephenson said that George is a "fantastic choice" for Sam, describing the character as "a complex and mysterious Bourne-style female spy unlike anyone we've seen on TV before".
Filming for Nemesis has started and will take place in Scotland, London and Morocco.