He was commissioned into the British Army as a cornet in 1792, became a lieutenant in 1793, and on 13 September 1794 was promoted lieutenant-colonel in the 114th Foot, a new regiment raised that year by his father.

[5] On 22 January 1808, the Tory Sir Arthur Wellesley, Chief Secretary for Ireland, wrote to the Duke of Richmond: The Parlt.

met yesterday... a drunken speech from Sheridan towards morning, and a blackguard one from Montague Mathew, who, with the figure of an Irish giant and the voice of a stentor, charged Perceval with treason to 5 millions of Irish Catholics & me with corruption at the Tipperary election....[2]On 5 May 1808, Mathew urged Wellesley and Perceval's government to increase its financial support for St Patrick's College, Maynooth, reminding them of a recent offer made by order of Napoleon Bonaparte to encourage Irish students to go from Lisbon to France for their education and promising them financial assistance.

[1] In 1815 the parliamentary sketch-writer Thomas Barnes wrote of Mathew that he showed "...all the characteristic fervour of his countrymen in favour of the cause of the Catholics, but at the same time evinces a blindness of blundering greater than even foolish illiberality ever ascribed to his nation".

The ingenious Burke, in his "Landed Gentry," traces this family back to Gwaithvoed the Great, Prince of Cardigan and Gwent...[11]