After academic studies, he traveled abroad until 1939 in Italy, France, Austria, Germany, Netherlands, Albania, Yugoslavia and Montenegro.
In 1920 he illustrated the book Tři muži se žralokem a jiné poučné historky (Three men with the shark and Other Stories) written by Jaroslav Hašek, writer and activist of the Anarchist Party, and author of the famous novel Osudy dobrého vojáka Švejka (The Good Soldier Švejk).
During the 1920s Košvanec increased its prestige, and in the meantime he married the painter Františka Matouškova, who later painted under the pseudonym Sidonie Matoušková-Košvancová.
The Czechoslovak Republic, was a bilingual country until 1945, and the German paper Prager Presse was published there from 1921 to 1938: on its pages Košvanec issued his satirical cartoons.
The cover of the book of Ivan Suk Little girls under the lantern (Holčičky pod lucernou, 1926) was illustrated with an impressive drawing, that expresses the light and the shade of the human and social complexity of the prostitutes' world.
This privileged relation enabled the artist to paint portraits of the most important characters of the First Republic such as the President Edvard Beneš, democratic statesman and politician during the transition period between the end of Habsburg Empire (1918) and the Communist takeover of February 1948.
Košvanec's paintings were more "praguese" at that moment: women appeared elegant, stylish, half-naked, surrounded by a flowering nature over the hills of Petrin, "in the greenish shade of wide gardens and leafy trees" in the quiet Hradcany, and these nymphs revealed the secret charm of Malá Strana and of St. Nicholas Church.
This theatrical gesture, which was judged to be outrageous, caused a collaborationism accuse and the immediate expulsion from the Association of Czech artists (Blok ceských výtvarníku) once the war finished.
On September 29, 1949, his wife died, he fell into a deep depression and suffered a total nervous breakdown that forced him to stay in a mental hospital.
He spent his last years in complete isolation until November 1961 when, at the age of 74, died forgotten by everybody and his body was buried in the cemetery of Olšany in Prague.