The Ben and Kate alum will play Curtis Holt, aka Mr. Terrific. Holt is a technological savant and inventor who works at Palmer Technologies under the supervision of Felicity Smoak (Emily Bett Rickards).
In the comics, Mr. Terrific’s alter-ego is Michael Holt, an extremely intelligent Olympic-level athlete who joined the justice Society of America following the death of his wife and unborn child.
Kellum’s casting comes on the heels of Neal McDonough joining the series as new villain Damien Darhk. Kellum will first appear in episode 2.
Arrow returns Wednesday, Oct. 7 at 8 p.m. ET on The CW.