Mary Howarth Arden was born in Liverpool, the daughter of Lieutenant-Colonel Eric Cuthbert Arden, of Heswall, Cheshire, a solicitor who had served with the Royal Garrison Artillery, and Mary Margaret (née Smith).

Her father and brother, Roger, joined the family firm which merged with Hill Dickinson in 2007.

As is customary, she was appointed a Dame Commander of the Order of the British Empire (DBE) at the same time.

[11][12] On entering her office, she took the judicial courtesy title of Lady Arden of Heswall.

She married Jonathan Mance (now Lord Mance, former Deputy President of the Supreme Court of the United Kingdom) in the Lady Chapel at Liverpool Cathedral in 1973; they have three children:[3] Arden's husband, Lord Mance, joined the Queen's Bench Division in October 1993, making them the first married couple to sit on the High Court bench.