Born in Gießen on March 29 1826 as the son of Hessian public official Ludwig Christian Liebknecht and Katharina Liebknecht (nee Hirsch), Liebknecht grew up with relatives after the death of his parents in 1832; from 1832 to 1842, he went to school at the Gymnasium of Gießen, then began studying philology, theology and philosophy in Gießen, Berlin and Marburg.
After working briefly as a teacher at the Musterschule of Friedrich Wilhelm Fröbel in Zürich and as a correspondent for the "Mannheimer Abendzeitung", Liebknecht took part in the revolutionary fights in Paris in February 1848; in September the same year, he was arrested in Baden and remanded following his involvement in the republican uprising of Gustav von Struve. Following his release in May 1849, he became a member of the Badische Volkswehr and an adjutant of Struve and fought in the Reichverfassungskämpfe ("federal constitution wars"); after the revolutionaries' defeat, he escaped to Switzerland and became a member of the Genfer Arbeiterverein (Worker's Association of Geneva), where he met Friedrich Engels.
In 1850, Liebknecht was arrested for his initiatives to unite Switzerland's German workers' associations and banished from the country, moving to his exile in London, where he stayed from 1850 to 1862 and became a member of the communist association, meeting Karl Marx in the process. He returned to Germany in 1862 after an amnesty for the participants in the revolution of 1848 / 1849 and became a member of Ferdinand Lassalle's ADAV (Allgemeiner Deutscher Arbeiterverein, "General German Workers' Association"), the precursor of the SPD.
From 1864 to 1865, Liebknecht also worked on the magazine "Der Social-Demokrat" ("the Social Democrat") published by Jean Baptist von Schweitzer; however, he soon found himself in disagreement with the paper's Prussia-friendly position, leaving the editorial staff and also being forced to leave the ADAV due to pressure from Schweitzer. After being evicted from Berlin, Liebknecht moved to Leipzig, where he met August Bebel, with whom he founded the Sächsische Volkspartei ("Saxon People's Party") in 1867 and the SDAP (Sozialdemokratische Arbeiterpartei Deutschlands, "Social Democratic Worker's Party of Germany") in 1869 in Eisenach. Liebknecht became one of the leaders of the SDAP and the leading publisher of the party organ, "Der Volksstaat" ("the People's State").
In 1872, Liebknecht, together with August Bebel, was sentenced to two years of Festungshaft ("imprisonment in a fortress") for high treason in a political prosecution known as the Leipziger Hochverratsprozess.
After being elected into the Reichstag in 1874, Liebknecht played a key role in the merger of the SDAP and ADAV into the SAPD (Sozialistische Arbeiterpartei Deutschlands, "Socialist Worker's Party of Germany") in Gotha in 1875; he also became publisher of the newly-founded party organ "Vorwärts" ("forward"), arguing for the integration of Marxist theories into the SAPD's program in his articles.
From 1878 to 1890, Liebknecht used his position as a Reichstag member to criticize the political situation even under Otto von Bismarck's "Sozialistengesetz" ("Socialists' law"); in 1891, he became editor-in-chief of "Vorwärts" and one of the originators of the SPD's new Marxist-inspired party platform. He also continued to appear at political conventions as a referent despite his advanced age until July 28 1900; in 1896, he was briefly jailed for four months after being convicted of lèse-majesté.