A member of the Hardenburg branch of the Leiningen family, Carl was born in Amorbach, the son of Prince Emich Carl of Leiningen (1763–1814) by his second marriage with Princess Victoria of Saxe-Coburg-Saalfeld (1786–1861). He was the only son, as Emich Carl's son by his first wife, Friedrich, had died in 1800.
Prince Emich Carl had received the Principality of Leiningen during the German mediatisation (Reichsdeputationshauptschluss) in 1803, as a compensation for the lost Hardenburg estates in the Palatinate occupied by French revolutionary troops, and took his residence at the secularised Amorbach Abbey. The princely territory, however, soonafter passed to the newly established Grand Duchy of Baden, the Kingdom of Bavaria and the Grand Duchy of Hesse. Prince Emich Carl died on 4 July 1814 and Carl succeeded him as third Prince of Leiningen. On 11 July 1818, his widowed mother married Prince Edward, the fourth son of King George III of the United Kingdom, at Kew Palace, Surrey. In 1819, Carl and his younger sister Princess Feodora were taken from Amorbach to London, where their half-sister Princess Victoria of Kent was born on 24 May at Kensington Palace.
On 13 February 1829, Carl married the Bohemian countess Maria von Klebelsberg (27 March 1806 – 28 October 1880), daughter of Count Maximilian von Klebelsberg and his wife Maria Anna von Turba. They had two sons:Ernst Leopold Victor Carl August Joseph Emich (9 November 1830 – 5 April 1904), who succeeded as the fourth Prince of Leiningen, and
Eduard Friedrich Maximilian Johann (5 January 1833 – 9 April 1914).
Carl had attended a private school in Bern and from 1821 onwards studied law at the University of Göttingen with the jurist Karl Friedrich Eichhorn, then one of the principal authorities on German constitutional law and leading proponent of the German Historical School of jurisprudence. At the British court, his multifaceted interests in art were aroused. From 1828, he had Waldleiningen Castle near Mörschenhardt (named after Waldleiningen in the Palatinate) erected as his private residence, a Romantic complex resembling Neo-Gothic castles in Britain, such as Abbotsford House. Carl was made a Knight of the Order of the Garter in 1837.
As a mediatized house, the Princes of the Leiningen were members of the Landtag diet in Baden, as well as in Bavaria and Hesse. Prince Carl became president of the Bavarian upper house (Reichsrat) in 1842 and also pursued a career in the Bavarian Army as Lieutenant general à la suite of the Cavalry. On 20 April 1842, he and 20 other noblemen gathered at Biebrich Palace, where they established the Adelsverein to organize the settlement of German emigrants in Texas; Carl was elected president of the society.
By the German revolutions of 1848–49, Leiningen had achieved much reputation as a liberal reformer and freethinker. He advocated the implementation of parliamentarism and openly criticized aristocracy's privileges; therefore, he was appointed Prime Minister of Revolutionary Germany by Regent (Reichsverweser) Archduke John of Austria on 6 August 1848. With a Catholic head of state and a Lutheran head of government, an equilibrium was reached in German dualism; moreover, Leiningen's close relations to the British Royal House were generally appreciated. His cabinet initially could rely on a liberal and left-wing majority in the newly established Frankfurt Parliament, however, as early as on 5 September, he resigned over the Schleswig-Holstein Question when in the First Schleswig War King Frederick William IV of Prussia unilaterally signed an armistice with Denmark at Malmö. The delegates of the Frankfurt assembly reacted with outrage and Leiningen, unable to assert the powers of the central authority, was forced to step down. He was succeeded by the Austrian politician Anton von Schmerling, who acted as Prime Minister until December.
In 1851, he also resigned as president of the Adelsverein and was succeeded by Prince Hermann of Wied. Shortly after his niece Victoria became engaged to Prince Frederick of Prussia, in 1855, he suffered a severe apoplectic attack. A second attack in November the following year was fatal, and he died at Waldleiningen Castle at the age of fifty-two, with his sister Feodora at his bedside.