Sikkar served in the Estonian War of Independence against post-revolutionary Soviet Russia on armoured train as a voluntary and an officer, he was granted a farm, which he held until 1944.
He finished economic faculty of Tartu University cum laude in 1936.
In 1920 he married Hilda Vilhelmine Truus (1900–1995) and had a son and a daughter.
In 1940 and 1944 he participated in resistance against Soviet and German occupations and escaped to Sweden September 12, 1944.
Because such political activities were then prohibited for Estonian exiles in Sweden, members of his government assumed their offices in Oslo, Norway.