"K.O." – his given names were rarely used – was born in Kristiansund. Here he trained as a typographer. He came to Trondheim as a journalist around 1900.
Most of his press career was spent with Ny Tid [New Time], where he was a journalist, and later editorial secretary for the paper, which was a Norwegian Labour Party organ. When the party was split in 1923, the majority in Trondheim consisted of those who looked to Moscow, and Ny Tid became the main organ for the Communist Party of Norway. Thornæs found his home in this wing, and he was the newspaper's editor until 1934.
Thornæs was an active man, not just as a member of the press. He helped dominate local politics in Trondheim for two decades, and he was a member of the board and chairman of the board of Trondheim Public Library during the final half of the 1930s. He also had artistic talents, as a musician and poet. He wrote quite a few poems, many of them printed in Ny Tid and in other papers. He also published Trompetskrald. Agitatoriske digte [Trumpet Blare. Agitating poems] in Trondheim in 1915, which contains his most well-known song lyric: Frem mot krigeraanden (Frem kamerater) [Forward against the warrior spirit (Forward Comrades)], also known as Antimilitaristisk sang [Anti-military song], first printed in Ny Tid 23 December 1911. This song has later become a regular part of the celebration of 1 May in Trondheim, to the tone of the rousing march composed by V. Ronander.
The memory of Thornæs continues to live in Trondheim, not least due to the park that bears his name. Not many people have had a park called after them in Trondheim. But Thornæsparken in the old working-class district of Møllenberg is known to most. This is also where Odd Hilt's granite statue of Thornæs from 1949 stands.
Recommended reading: Livet er mulig! [Life is possible] Rune, 1978.