Stephanie was born in London, in February 1984 to a Greek Cypriot father and a British mother with both English and Welsh ancestry.
Leonidas started acting in community theatre when she was eight; at nine she acquired an agent and began to work in television. Notable credits include the television drama, Daddy's Girl
, the soap opera, Night and Day
and a 2004 episode of Doc Martin
in which she plays Melanie, a local Portwenn 15-year-old girl who develops an unhealthy fascination with the surgeon. In 2005 she starred in Neil Gaiman and Dave McKean's MirrorMask
in the dual roles of Helena and the Dark Princess, and followed this with roles in a BBC adaptation of Dracula
, as well as Crusade in Jeans
. Her theatrical roles have included Adela in a production of Lorca's The House of Bernarda Alba
, and Dani in The Sugar Syndrome
, staged in 2003.
She has also starred in the BBC made for TV film Atlantis
(2011). In 2011, she was in a play for the Transatlantyk Festival called Influence
, written by Shem Bitterma. Currently, Stephanie stars as Irisa Nyira in the new science fiction show Defiance.