Nils Klein’s father worked as a land surveyor. He himself was trained as a forester at the Kloten forest school in Örebro province, where he later also worked as an assistant teacher. In 1909 he was awarded a travel grant to visit demonstration forests in Germany. Klein was promoted to the rank of county forester, in which position he was transferred to various parts of Sweden. His appearance in the trap event at the 1912 Olympics was rather disappointing when he placed second to last of the 61 competitors.