[4] In 1939 he supported the merger between the workers' and bourgeois sports organizations, in order to create a unity front against fascism.

The Nazis had an active provocateur and infiltrator in Trøndelag, Henry Rinnan, who managed to unveil most of the communist resistance leaders in the district in October and November 1941.

From early 1942 Thingstad became a part of the district leadership and underground central committee of the Communist Party.

[5] A German court-martial sentenced him to death on 4 May 1943, and he was executed at Kristiansten Fortress together with ten other people on 19 May.

[1][3] Tore Pryser's book Klassen og nasjonen 1935-1946 featured a goodbye letter Thingstad wrote in his cell.