Thomas was a successful Silk manufacturer who descended from a cadet branch of Mac Raghnaill chiefs of Lough Scur in County Leitrim.
[2] In the 1820s, he supported the pro-Catholic agitation in Roscommon led by his father, the O’Conor Don, later that decade and assisted in his return for the county, following the granting of emancipation, in 1830.
He moved the resolution for repeal of the legislative Union with Britain at a county meeting, on 14 January 1831, and seconded one in favour of parliamentary reform at another, on the 16 April 1831.
I really know no one individual to whom the Catholics of Ireland are so powerfully indebted for the successful result of their contest for emancipation ... His was not holiday patriotism ... No, in the worst of times and when the storms of calumny and persecution from our enemies and apathy and treachery from our friends raged at their height he was always found at his post.
O'Connell spoke well but blandly of O'Conor and Charles Wood, joint Parliamentary Secretary to the Treasury, termed him ‘a gentleman, not wise but worth attention and civility’.
On 27 August 1824, he married his first cousin once removed Mary Blake (died 1841), daughter of Major Maurice Blake, of Towerhill house, in County Mayo, and Maria O'Connor, daughter of the wealthy catholic merchant Valentine O'Connor, from a cadet branch of the O'Conor Sligo who had settled in Galway and Mary Moore.