He was a student of Ivan Grevs, graduated from the Faculty of History and Philology of Saint Petersburg State University.

Karsavin was expelled in November 1922, together with a group of forty-five scientific and cultural figures (Nikolai Berdyaev, Sergei Bulgakov, Semyon Frank, Ivan Ilyin and others) and their family members to Germany (see Philosophers' ships).

While living in Lithuania, he edited academic publications and published his own books in Russian, On Personality (1929) and A Poem on Death (1931).

Karsavin was arrested and accused of "participating in the anti-Soviet Eurasianist movement and preparing to overthrow the Soviet state".

This happened thanks to the personal archive of the widow of Anatoly Vaneev [ru], a disciple of Karsavin, which preserved a photograph at the grave marked П-11, as well as the testimony of former prisoners of the Abez camp.

In December 1992, on the occasion of his 110th birthday anniversary, on the house at Krėvos Street 7 in Kaunas, where Karsavin lived in 1935–1940, a memorial plaque was installed.

[10] In October 2005, a bilingual marble memorial plaque by sculptor Romualdas Kvintas [lt; ru] was installed on the façade of the house on Didžioji Street in Vilnius, where Karsavin lived from 1940 to 1949.

Selected treatises and poetry were included in a Lithuanian edition compiled by poet and translator Alfonsas Bukontas.

[13] His based on extensive material works of the early period are devoted to the history of medieval religious movements and the spiritual culture of the Middle Ages.

He drew on early Christian teachings (Patristics, Origen) and Russian religious philosophy, especially the tradition of Vladimir Solovyov.

For Karsavin, the idea of all-unity was understood as a dynamic principle of the formation of being and as a fundamental category of the historical process lying at the heart of historiosophy.

It is understood as a supreme existence in God, whereas real, earthly life is called бывание (presence; attendance), which emphasizes its finitude, its imperfection.

However, they can become part of the Divine Hypostasis by dedicating their lives to the process of deification, that is, to an existence analogous to the life of Christ.