Several of his elder brothers also took part in the rebellion, some of whom died fighting. Another, Brian MacArt O'Neill, was hanged for manslaughter in 1607. One of his nephews was Daniel O'Neill, a Protestant who became a noted cavalier in England during the 1640s. Another of his nephews, Hugh Duff O'Neill fought in the Confederate Wars and famously inflicted heavy casualties on Oliver Cromwell's New Model Army during the Siege of Clonmel in 1650.