O'Hegarty resigned his military duties in April 1921, being replaced as Director of Organisation by Eóin O'Duffy, to concentrate on his work in the Dáil secretariat.
Frank Pakenham in "Peace by Ordeal" describes Diarmuid O'Hegarty as, the "civil servant of the revolution," the man perpetually behind the scenes, could conceal from few who met him the gifts that were to make possible the Irish constitutional achievements at the Imperial Conference of 1926 '.