Louis Charles de La Trémoille (26 October 1838 – 4 July 1911), 9th duc de Thouars, was a French nobleman and the son of Charles Bretagne Marie de La Trémoille and his third wife, Valentine Eugénie Joséphine Walsh de Serrant.
La Trémoille was born in his father's seventy-fifth year, and acceded to his titles just one year later. He became an historian and was a member of the Académie des inscriptions et belles-lettres. He devoted much study to his family archives, and granted access to them to researchers, in particular Paul Marchegay (1812–1885) and the historian Hugues Imbert (1822–1882).
On 2 July 1862 he married Marguerite-Jeanne Tanneguy-Duchâtel (16 December 1840 - 19 September 1913), daughter of count Charles Marie Tanneguy Duchâtel, former minister to King Louis-Philippe of France. They had two children:
Louis Charles Marie (1863–1921) who succeeded him, and
Charlotte (1864–1944); who married the duke of Estrées, Charles Marie François de La Rochefoucauld (1863–1907).