Clark, who quit LWT last January after complaining ITV was not taking enough risks with new shows, is currently an executive producer in BBC entertainment production, where she has been developing a number of projects.
Her past credits include stints on Don't Forget Your Toothbrush, The Big Breakfast, Families at War and All Rise for Julian Clary. She will take up her new role in mid-February.
Vardanis, who is overseeing Lush's former post, will move to entertainment only after a new controller of daytime is appointed.
She has previously commissioned daytime factual shows under controller of factual commissioning Nicola Moody and series produced Passport to the Sun.
The pair, who replace John McHugh and Jane Fletcher who quit to join Channel 4 and RDF Media respectively, will both report to Lush. Lush took over the entertainment post last month.