On 22 July 1852 she was married at Hanover to Viscount Mandeville, eldest son of the 6th Duke of Manchester. He succeeded his father as 7th Duke of Manchester on the 8 August 1855, and Louisa became Duchess of Manchester.
They had five children:
George Victor Drogo Montagu, 8th Duke of Manchester (1853–1892)
Lady Mary Louisa Elizabeth Montagu (Kimbolton Castle, 27 December 1854 – 10 February 1934), married firstly at Kimbolton Castle, 10 December 1873 William Douglas-Hamilton, 12th Duke of Hamilton and had issue, and secondly 20 July 1897 to Robert Carnaby Forster of Easton Park, Wickham Market, Suffolk (d. 23 June 1925), without issue.
Lady Louisa Augusta Beatrice Montagu (Kimbolton Castle, 17 January 1856 – London, 3 March 1944), married London, 10 August 1876 Archibald Acheson, 4th Earl of Gosford and had issue.
Lord Charles William Augustus Montagu (Kimbolton Castle, 23 November 1860 – 10 November 1939), married at Kimbolton Castle, 4 December 1930 Hon. Mildred Cecilia Harriet Sturt (27 February 1869 – London, 17 September 1942), daughter of Henry Sturt, 1st Baron Alington, without issue.
Lady Alice Maude Olivia Montagu (London, 15 August 1862 – Coworth Park, 23 July 1957), married at London, 5 January 1889 Edward Stanley, 17th Earl of Derby and had issue.
She was appointed Mistress of the Robes to the Queen on 24 February 1858, and remained in that office until the fall of Lord Derby's government on 11 June 1859.
The Duke of Manchester died at Naples on 22 March 1890.