The International Mathematical Union said Viazovska, who holds the chair in number theory at the Swiss Federal Institute of Technology Lausanne, was being honored for her work on the densest packing of identical spheres in eight dimensions.
The other winners were French mathematician Hugo Duminil-Copin of the University of Geneva; Korean-American mathematician June Huh of Princeton; and British mathematician James Maynard of the University of Oxford.
The Fields Medal is awarded every four years to mathematicians under age 40. The recipients are normally announced at the International Congress of Mathematicians, which was originally due to be held in Russia this year but moved to Helsinki instead.
“The ongoing barbaric war that Russia still continues to wage against Ukraine clearly shows that no other alternative was feasible," the president of the International Mathematical Union, Carlos E. Kenig, said.