[note 2] In 1634 he was elected as a member of parliament for County Clare replacing his cousin Barnabas O'Brien whose stay in England had been protracted.

With Donough still a minor at his father's death, the dispute on the ownership of Dromoland was thus continued by Donough's mother Slaney O'Brien and apparently settled by arbitration in 1613 with the Earl becoming owner and agreeing to pay £132 13s 4d in compensation to Slaney O'Brien.

Donough continued to contest his claim on Dromoland through the Court of Wards and Liveries in Dublin after the Earl's death in 1626 and in 1629 was granted entry "on all the manors, lands and tenements of his late father" on payment of a fine.

Henry O'Brien, 5th Earl of Thomond did however transfer two other properties to Donough as compensation.

[3][4] He married Honora (1607 [sic][note 3]-1637), daughter of Richard Wingfield of Robertstown, Limerick.