Sir Mark John MacTaggart-Stewart, 1st Baronet (12 October 1834 – 26 September 1923), known as Mark John Stewart until 1880, was a Scottish Conservative Member of Parliament in the House of Commons of the United Kingdom. He represented Wigtown Burghs from 1874 to 1880 and again for a few months later in 1880 and also sat for Kirkcudbrightshire between 1885 and 1906 and briefly in 1910.

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He married in 1866 Marianne Susanna Ommanney, daughter and heiress of John Orde Ommanney (d.1846), who was a son of Sir Francis Molyneux Ommanney. Her mother Susanna MacTaggart was a daughter of Sir John McTaggart, 1st Baronet, and through her they inherited an estate at Ardwell.^[1] In 1905 he assumed the additional surname of MacTaggart as he and his wife took possession of the Ardwell estate of her grandfather.^[2] He was an officer in the 1st Ayrshire and Galloway Artillery Volunteers and was appointed their Honorary Colonel on 22 December 1888.^[3]

On 7 October 1892, he was made a Baronet, of Southwick in the Stewartry of Kirkcudbright and Blairderry in the County of Wigtown.^[4] MacTaggart-Stewart died in September 1923, aged 88. He was succeeded in the Baronetcy by his only surviving son, Sir Edward Orde MacTaggart-Stewart, 2nd Baronet.^[2]

Sir Mark and Lady MacTaggart-Stewart had five daughters and one son:^[5]

• Janet Gertrude McTaggart-Stewart (b.1871), married in 1899 Robert George Seton (b.1860), a descendant of the Barons Brownlow, and left children.
• Sarah Blanche McTaggart-Stewart (b.1872).
• Frances Emily McTaggart-Stewart (1873–1949), married in April 1903 Archibald Kennedy, Earl of Cassilis (1872–1943), who succeeded in 1938 as Marquess of Ailsa. They left no children.
• Susanna Mary McTaggart-Stewart (1878–1961), married first in 1901 Archibald Patrick Thomas Borthwick, 20th Lord Borthwick (1867–1910), and secondly in 1916 Alfred FitzRoy, 8th Duke of Grafton, leaving daughters by both husbands.
• Margaret Anna McTaggart-Stewart (1880–1962), married in 1906 (div. 1919) Sir David Charles Herbert Dalrymple, 2nd Baronet (1879–1932), and had children.
• Edward Orde McTaggart-Stewart (1883–1948), who succeeded as 2nd and last Baronet, leaving two daughters by his wife married in 1917 Hon. Margaret Selina Flora Maud Clifton-Hastings-Campbell (1895–1975), daughter of the 3rd Baron Donington.