Ifans is to play Sherlock Holmes' older brother, Mycroft, in Season 2 of the show, which returns Sept. 26. Jonny Lee Miller plays brilliant private detective Sherlock on the series, while Lucy Liu plays his assistant, Joan Watson.
The Season 2 premiere will be the first "Elementary" episode shot on location in London.
"In the episode, Sherlock is called to London to revisit an old case, where he is forced to face his older brother, Mycroft," a synopsis said. "Although the siblings suffered a drastic falling-out a few years earlier, Mycroft allows Sherlock and Joan to stay in his new home, 221B Baker Street. With Joan in the middle, the brothers are forced to confront their very complicated history."
"I could not be more excited to have Rhys coming aboard," series executive producer and creator Robert Doherty. "I've always been a tremendous fan and feel very honored to have him in the fold. Equally excited are Jonny and Lucy, both of whom have worked with Rhys in feature films. I think this is going to be a lot of fun for all of us."
Ifans' film credits include "The Amazing Spider-Man," "Notting Hill" and "Anonymous."