The house looked over the Dartrey estate, owned by Edward's father's cousin and benefactor, Thomas Dawson, 1st Viscount Cremorne (1725–1813).
It was named for Lord Cremorne's new wife, Philadelphia Hannah Freame, granddaughter of William Penn of the Province of Pennsylvania.
Rather than abandon his plans for a career in law, Mayne passed the responsibility of running the estate to his younger brother, William, providing him with legal advice when needed.
After a lengthy and successful career as a barrister in Dublin, in 1805 he was appointed a Judge of Court of Common Pleas (Ireland).
A list of the sentences he passed in 1815 (kept at the Old Court House, Downpatrick Museum) includes a number of death sentences—one for stealing a horse.