[1] Kaarna was born in Artra, Palupera Parish, Kreis Dorpat (now Elva Parish) to farmers Jaan and Liisa Kaarna (née Tullino).
[2][3] Between 1918 and 1920, Kaarna was Commissar of the Estonian Provisional Government in Narva and Virumaa.
In addition, he was a member of the Riigikogu from 1920 until 1929 in the I, II, and III Riigikogu, representing the Estonian Labour Party; Ernst Raatma succeeded him after he left.
He was the chairman of several organizations, such as the Narva Estonian Society, one of the founders and chairman of the Joala Mutual Credit Union, a member of the board of the Estonia Society, and an assistant chairman of the congregation of the Estonian Evangelical Lutheran Church's Kaarli Church on Toompea.
[4] Following the Soviet occupation of Estonia in 1940, Kaarna was arrested by the NKVD on 18 September 1940 and died in imprisonment in the gulag in Karaganda.