Known best for her series regular role as Irisa Nyira on the Syfy series Defiance, Leonidas also acted in episodes of such British television shows as Holby City and Eternal Law. In addition, she played major roles in several made-for-TV films, including Daddy's Girl and Ordeal by Innocence. Before beginning her screen acting career at the age of nine, she appeared in several community theater productions. She later acted in professional stage productions of The Sugar Syndrome and Influence.