[2][3][4] He was the son of Timothy O'Brien and his wife (née Madden).
In 1844, O'Brien was made Lord Mayor of Dublin, a position he again held in 1849.
Becoming an Independent Irish MP in 1852[3] and a Whig in 1857,[4] he held the seat until the 1859 general election, when he did not seek re-election.
Upon his own death in 1862, the baronetcy was inherited by his son, Patrick O'Brien.
[6] Outside of his political career, O'Brien was also a Justice of the Peace and a Deputy Lieutenant.