The three-part series - from Public Enemies and Garrow's Law writer Tony Marchant - was first announced in January.
Leaving will focus on the relationship between disillusioned 25-year-old Aaron (Turner) and unhappy 45-year-old wife and mother Julie (McCrory).
When the pair begin working together at a Cheshire country house hotel, they share an intimate moment which takes them both by surprise and must face the consequences of their actions.
McCrory's recent credits include the role of Narcissa Malfoy in Harry Potter and the Deathly Hallows and BBC Four's Jean Shrimpton biopic We'll Take Manhattan.
She and Turner are joined by Deborah Findlay (Cranford), Nick Dunning (The Iron Lady), Charity Wakefield (Casualty 1909) and Bart Edwards (EastEnders).
Amelia Young (United), Sean Gallagher (Coronation Street), Gregg Chillin (Being Human) and Celyn Jones (Above Suspicion) will also star.
Juliet Charlesworth (Clocking Off) will serve as producer, while Gaby Dellal (Angels Crest) will direct.
Leaving is produced by Red Production Company (Scott & Bailey, Exile) for ITV1, with filming currently under way in Manchester and Cheshire.
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