Hardcastle is married to the actor Tom Wilkinson, with whom she has two children, Alice born in 1989 and Molly born in 1992.
In 2011, Hardcastle and actor Tom Wilkinson, her husband, portrayed real life husband and wife Joe and Rose Kennedy in the mini series The Kennedys.
In 2012, she had a supporting role in the film The Best Exotic Marigold Hotel, in which her husband starred (their characters did not interact), and a returning role in the 2015 sequel The Second Best Exotic Marigold Hotel. Wilkinson and Hardcastle again played husband and wife in Good People (2014).
