McElligott most recently appeared on the TV shows The Last Tycoon and House of Cards.
According to Deadline, Antony Starr has been cast as Homelander, leader of The Seven.
Starr is perhaps best known for his roles on the TV shows American Gothic and Banshee.
Nathan Mitchell rounds out this faux-Trinity as Black Noir, a mysterious member of The Seven who is almost always shown in silhouette with his face obscured.