Baron Louis Gerhard De Geer of Finspång (18 July 1818 – 24 September 1896) was a Swedish statesman and writer.

De Geer was born at Finspång manor. He was a lawyer, and in 1855 became president of the Göta Hovrätt, or lord justice for the appellate court of Götaland. From 7 April 1858 to 3 June 1870 he was Prime Minister of Justice. As a member of the nobility he took part in the Swedish Riksdag of the Estates from 1851 onwards. From 1867 to 1878 he was the member for Stockholm in the first chamber in the New Riksdag, and introduced and passed many useful reforms.

His son Louis De Geer was also prime minister of Sweden for a short period.

His greatest achievement was the reform of the Swedish representative system. The reforms introduced a bi-cameral elected parliament replacing the existing cumbersome and less democratic representation by estates, a hangover from the later Medievel Times. This measure was accepted by the Riksdag in December 1865, and received the royal sanction on 22 June 1866. For some time after this De Geer enjoyed considerable popularity. He retired from the ministry in 1870, but took office again, as minister in 1875.

In 1876 he became the first Prime Minister of Sweden and served until April 1880, when the failure of his repeated efforts to settle the armaments question again induced him to resign. From 1881 to 1888 he was Chancellor for the Universities of Uppsala and Lund. He was an advocate of free trade and economic liberalism and some argue laid the foundations for the strong economic growth in Sweden from 1870 to 1970.

Besides several novels and aesthetic essays, De Geer has written a few political memoirs of supreme merit both as to style and matter, the most notable of which are: Minnesteckning öfver A. J. v. Höpken (Stockholm, 1881); Minnesteckning öfver Hans Järta (Stockholm, 1874); Minnesteckning öfver B. B. von Platen (Stockholm, 1886); and his own Minnen (Stockholm, 1892), an autobiography, invaluable as a historical document, in which the political experience and the matured judgments of a lifetime are recorded with singular clearness, sobriety and charm. For example, his explanation of why he, at such a young age, was appointed prime minister, was that in the narrow circles of Swedish nobility at the time, it was difficult to find anyone with at least the mediocre intelligence which was needed for the office.

De Geer was a member in the Swedish Academy from 1862, on Seat 17. In 1862, he was also elected a member of the Royal Swedish Academy of Sciences.