In 1822 he succeeded his half-brother as 3rd Marquess of Londonderry, inheriting estates in the north of Ireland where, as an unyielding landlord, his reputation suffered in the Great Famine.

[citation needed] In 1795 his father was created Viscount Castlereagh[9] and in 1796 Marquess of Londonderry in the Irish peerage.

[10] In 1800, Charles Stewart was elected in the Tory interest to the Irish House of Commons as member of parliament for Thomastown borough, County Kilkenny, in place of George Dunbar,[11] and after only two months exchanged this seat for that of County Londonderry,[12] being replaced at Thomastown by John Cradock.

In July 1814 he was summoned to the House of Lords and replaced as MP for Londonderry by his uncle Alexander Stewart of Ards.

[15] On 8 August 1804 at the church of St George's, Hanover Square, London, Charles Stewart married Lady Catherine Bligh.

[citation needed] When British troops returned to the Iberian Peninsula after the Corunna Campaign, they were commanded by Sir Arthur Wellesley (later the Duke of Wellington).

[26] He also excelled at Bussaco in September 1810 and at Fuentes de Oñoro (May 1811) where he took a French Colonel prisoner in single combat.

From May 1813 until the end of the war, Sir Charles was Envoy Extraordinary and Minister Plenipotentiary to Berlin,[32] and was also Military Commissioner with the allied armies, being wounded at the Battle of Kulm in August 1813.

[33] In the same year, he received honorary degrees from Oxford and Cambridge, was admitted to the Privy Council, and was appointed a Lord of the Bedchamber to the king.

He was not well regarded as he made a spectacle of himself with his loutish behaviour, was apparently rather often inebriated, and frequented prostitutes quite openly.

As the great powers were taking an increasingly reactionary approach, the British government sent Lord Stewart to observe, but not participate in the decisions.

Before the end of his diplomatic career Lord Stewart had, on 3 April 1819, married his second wife, Lady Frances Anne Vane-Tempest, daughter and heiress of Sir Henry Vane-Tempest,[36] at her mother's house in Bruton Street, Mayfair, and took her surname of Vane, by Royal licence, as had been stipulated in her father's will.

[40] Lord Londonderry used his new bride's immense wealth to acquire the Seaham Hall estate in County Durham, developing the coalfields there.

[citation needed] In 1836 the Orange Order was accused of plotting to place Ernest Augustus, Duke of Cumberland and Imperial Grand Master of the Orange Order, on the throne in place of Victoria when his brother King William IV died.

[41] Under pressure from Joseph Hume, William Molesworth and Lord John Russell, the King indicated measures would have to be taken and the Duke of Cumberland was forced to dissolve the Orange lodges.

In July 1832, the Marquess had received a letter from Lieutenant-Colonel W. B. Fairman, the Deputy Grand Secretary of the Orange Institution of Great Britain, advising him that following "a death of importance" (the passing of the King) the Orangemen would abandon their policy of "non-resistance" to the present "Popish Cabinet, and democratical Ministry" (the parliamentary reform ministry of Earl Grey) and that "it might be political" for the Marquess to join them.

Noting that there were already Orange lodges in Newcastle, South Shields, and Darlington, Fairman also suggested to Londonderry that to assume the role in Durham of County Grand Master might be advantageous to him "in a personal sense": his "pitmen" (the miners employed in his collieries) might be induced to organise lodges among themselves which would "prove a partial check against their entering into cabals [i.e. trade unions] hereafter".

[43] While he conceded that he wished the government should do more to check "the baneful influence of the Liberal and Radical associations", including trade unions, Londonderry went to some length in the House of Lords to deny any possible connection between himself and "the alleged project for altering the succession to the throne".

He had also spoken with Lord Kenyon (his then house guest, who had led opposition to Catholic Emancipation)[45] and had "no doubt" he would "convince his Royal Highness" (the Duke of Cumberland), as well as Fairman, "that the present moment is not the time when the object can be forwarded.

[48]By the time of the outbreak of the Great Irish Famine in 1845, Londonderry was one of the ten richest men in the United Kingdom.

While many landlords made efforts to mitigate the worst effects of the famine on their tenants, Londonderry was criticised for meanness: he and his wife gave only £30 to the local relief committee but spent £15,000 renovating Mount Stewart, their Irish home.

[49] In contrast to his neighbour, the Marquess of Downshire, he rejected rent reductions (for which he was excoriated by James MacKnight in the Presbyterian weekly, the Banner of Ulster).

When Wellington, whom he admired greatly, died in 1852, his place as Knight of the Garter was given to Londonderry,[54] who was officially invested on 19 June 1853.

[58] Two-thirds of the cost of the tower was met by 98 subscribers (in a list headed by Emperor Napoleon III) most of whom were fellow gentry.