The legal drama will star Patrick J. Adams as Mike Ross, a brilliant but unmotivated college student who is recruited to a top Manhattan law firm by lawyer Harvey Specter (Gabriel Macht) despite his lack of a law degree.
Markle will play Rachel Lane, a young lawyer "with an encyclopedic knowledge of the law" who is assigned to Mike, according to The Hollywood Reporter.
The actress has previously featured on Fringe and recently appeared in film Get Him To The Greek.
Former Firefly star Gina Torres has also been cast as Katherine Pearson, a senior partner at the law firm. However, the role is in second position to her commitment on ABC Family series Huge.
Rick Hoffman will also appear in the pilot as a jealous lawyer.