He worked for many years as a professor and administrator at Charles University, and helped found the Czechoslovak Academy of Sciences.

He has been called "probably the first Czechoslovak mathematician whose scientific works received wide and lasting international response".

české vyšší reálné gymnasium, Ječná, Prague), so when he entered Charles University in 1915 he had to do so as an extraordinary student until he could pass a Latin examination three semesters later.

After completing his studies, he became an assistant to Jan Vojtěch at the Brno University of Technology, where he also met Mathias Lerch.

Notable among these are Miroslav Katětov, a chess master who became rector of Charles University, Jaroslav Kurzweil, known for the Henstock–Kurzweil integral, Czech number theorist Bohuslav Diviš, and Slovak mathematician Tibor Šalát.

[1] Although Jarník's 1921 dissertation,[1] like some of his later publications, was in mathematical analysis, his main area of work was in number theory.

One of Jarník's theorems (1926), related to this problem, is that any closed strictly convex curve with length L passes through at most points of the integer lattice.

Neither the exponent of L nor the leading constant of this bound can be improved, as there exist convex curves with this many grid points.

He proved (1928–1929) that the badly approximable real numbers (the ones with bounded terms in their continued fractions) have Hausdorff dimension one.

He also considered the numbers x for which there exist infinitely many good rational approximations p/q, with for a given exponent k > 2, and proved (1929) that these have the smaller Hausdorff dimension 2/k.

In this problem, one must again form a tree connecting a given set of points, with edge costs given by the Euclidean distance.

[1] The Vojtěch Jarník International Mathematical Competition, held each year since 1991 in Ostrava, is named in his honor,[16] as is Jarníkova Street in the Chodov district of Prague.