He was educated at Downside School, Stonyhurst College and Christ Church, Oxford.
He then spent time at the Université catholique de Louvain, before travelling in Germany. In 1849, he succeeded his father as baronet. The first issue appeared on 23 March 1867, but its outspoken support for the Irish Home Rule movement made it unpopular.
The last issue was published on 13 February 1868.
He was High Sheriff of Kerry in 1866. His early support for Home Rule turned into opposition during the 1870s and he spoke openly against the politics of Charles Stewart Parnell.
After leaving Parliament, Blennerhassett continued to be active in Irish public affairs He contributed regularly to The Times and The Daily Telegraph and was a Justice of the Peace.
In 1905, he was sworn of the Privy Council of Ireland.
In October 1901 he was awarded an honorary doctorate (Doctor of Laws) by the Royal University of Ireland.
19th United Kingdom Parliament. 20th United Kingdom Parliament. 22nd United Kingdom Parliament]
Blennerhasset sat as a Liberal Member of Parliament for Galway Borough from 1865 to 1874 and for County Kerry from 1880 to 1885.