He is remembered chiefly as co-executor and legatee of Esther Vanhomrigh, the beloved "Vanessa" of Jonathan Swift, although he was not a close friend of hers; indeed it is possible that they never met.
[1]: 141 He was born in Clonmel, County Tipperary, son of John Marshall, styled as a "gentleman" and his wife Catherine.
[1]: 209 He was educated at Clonmel Free School and Kilkenny College, entered Middle Temple in 1718 and was called to the Irish Bar in 1723.
[1]: 209 He purchased a house at the at that time fashionable number 20 Dominick Street in 1758 from the painter and property developer Robert West.
His practice was lucrative, though the bulk of what became a great fortune was undoubtedly due to his advantageous marriage to Mary Wooley.