David, born about 1550, was the son of James de Barry, 4th Viscount Buttevant and the Lady Ellen MacCarthy Reagh, illegitimate daughter of Cormac na Haoine MacCarthy Reagh, 10th Prince of Carbery. He married firstly the Lady Ellen Roche, daughter of David Roche, 5th Viscount Roche of Fermoy, by the Lady Ellen Butler, daughter of James Butler, 10th Baron Dunboyne.
At the outbreak of the Desmond Rebellions, his father, the then Viscount Buttevant, supported the rebels and in the subsequent confiscations of his estates, the friary in Buttevant, together with its glebe, passed into the hands of the poet, Edmund Spenser. He was noted for his long and bitter feud with Sir Florence MacCarthy, the MacCarthy Mór, whose loyalty to the Crown was always suspect. De Barry did great damage to his reputation by spreading rumours about MacCarthy"s alleged acts of treason, in particular his links with Patrick O"Collun whom MacCarthy had once employed as a fencing master.
In 1594 O"Collun was executed for conspiracy to kill Queen Elizabeth I. As a result, MacCarthy spent much of his later life in custody.
In 1601, during the Nine Years War the viscount sided with the new President of Munster, Sir George Carew. In the wake of the Battle of Kinsale, he was granted large estates in Munster which had been forfeited by the MacCarthys.
He died at Barryscourt Castle 10 April 1617.
