Opposed to the restoration of a parliament in Dublin, his defence of Ireland's union with Great Britain emphasised what he conceived as the liberal virtues of British imperial administration.

[6] That same year, he married his friend's cousin, Letitia, co-heiress to the mercantile fortune of her father, the Belfast merchant-patrician (and former United Irishman) William Tennent.

[7] Following the Reform Act 1832, both he and Robert Tennent decided to contest the first open election for the two-seat Belfast constituency, previously in the "pocket" of the town's proprietor, Lord Donegall.

Replying to Daniel O'Connell in the 1834 Commons debate on Repeal of the Union, Emerson Tennent sought to eschew the Protestant sectionalism and fear of Catholicism, generally assumed to be the central elements of unionist thought.

[11] Reflecting on the recent vote to suppress slavery in the British Empire, he remarked:[10]I shall never fail to regard it as a proud distinction that I have myself been enabled, during the course of the last twelve months, to contribute my own humble vote, to extend the blessings of freedom from the confines of India to the remotest shores of the Atlantic; to liberate the Hindoo, and to strike off the fetters of the African.

These are the triumphs beyond the reach of a 'Local Legislature'...toward which the highest ambition of an Irish Parliament could never soar; these are the honours which enable our birth-place as Irishmen, to add to our distinctions the glory of being Britons.At the end of 1845, his promising parliamentary career (in 1841 he had been made Secretary to the Board of Control) came, temporarily, to end when he realised that his strong support for Catholic civil and political equality in Ireland had compromised his chances of re-election from Belfast.

In a response to an economic depression that severely affected growers and merchants for coffee and cinnamon, he persuaded Earl Grey, Secretary of State for Colonies in London to shift the burden of the colony's tax revenue from export duties to imposts on guns, dogs, carts, and shops, and to a tax to be paid in lieu of compulsory labour on plantation roads.

The policy sharpened the plight of the progressively dispossessed peasantry and increased the pressure upon them to submit to wage labour, their resistance to which had forced cash-crop planters to import large numbers of Tamil "coolies" from southern India.

His family consisted of two daughters and a son, Sir William Emerson Tennent, who was an official in the Board of Trade, and at whose death the baronetcy became extinct.