Schmitt's work has attracted the attention of numerous philosophers and political theorists, including Walter Benjamin, Leo Strauss, Jürgen Habermas, Friedrich Hayek, Jacques Derrida, Hannah Arendt, Susan Buck-Morss, Giorgio Agamben, Jaime Guzmán, Antonio Negri, Slavoj Žižek and Avital Ronell among many others.
Schmitt was born in Plettenberg, Westphalia, German Empire. His parents were Roman Catholics from the German Eifel region who had settled in Plettenberg. His father was a minor businessman. He studied law at Berlin, Munich and Strasbourg and took his graduation and state examinations in then-German Strasbourg during 1915. His 1915 doctoral thesis was titled Über Schuld und Schuldarten (On Guilt and Types of Guilt).
He volunteered for the army during 1916. The same year, he earned his habilitation at Strasbourg with a thesis under the title Der Wert des Staates und die Bedeutung des Einzelnen (The Value of the State and the Significance of the Individual). He then taught at various business schools and universities, namely at the University of Greifswald (1921), the University of Bonn (1921), the Technische Universität München (1928), the University of Cologne (1933), and the University of Berlin (1933–1945).
During 1916, Schmitt married his first wife, Pavla Dorotić, a Serbian woman who pretended to be a countess. They were divorced, though an appeal to the Catholic Church for an annulment was rejected. During 1926 he married his second wife, Duška Todorović (1903–1950), also Serbian; they had one daughter, named Anima. Subsequently, Schmitt was excommunicated because his first marriage had not been annulled by the Church. His daughter Anima Schmitt de Otero (1931–1983) was married, from 1957, to Alfonso Otero Valera (1925–2001), a Spanish law professor at the University of Santiago de Compostela and a member of the ruling Spanish Falange party under the Franco régime. She translated several works by her father into Spanish. Letters from Carl Schmitt to his son-in-law have also been published.
As a young man, Schmitt was "a devoted Catholic until his break with the church in the mid twenties." From around the end of the First World War, he began to describe his Catholicism as "displaced" and "de-totalised". Consequently, Gross argues that his work "cannot be reduced to Roman Catholic theology given a political turn. Rather, Schmitt should be understood as carrying an atheistic political-theological tradition to an extreme." Schmitt met Mircea Eliade in Berlin during the summer of 1942 and spoke later of Eliade to his friend Ernst Jünger and of his interest to Eliade's works.