He was a son of Frithjof M. Plahte (1836–1899) and Marie, née Birch (1852–1937). He was a brother of Herbert and Erik Plahte, and an uncle of Frithjof M. Plahte, Junior. and Hans Barthold Andresen Butenschøn, Junior. His father had settled at Høvik in Bærum, and Viktor lived there.
He also attended Oslo Commerce School.
He was however born in Surrey, and took practical business training in England as well as in Sweden. The bank changed its name to Andresens Bank in 1913 and merged with Bergens Kreditbank in 1920. The merger was dissolved later in the 1920s.
Plahte sat as co-owner and bank director from 1912 to 1923.
He also founded Christiania Portland Cementfabrik together with Donato Brambani. He chaired the Norwegian Bankers" Association from 1919 to 1921, as well as Christiania Portland Cementfabrik.
There is a road in Bærum named Viktor Plahtes vei. However, it is named after Viktor"s son, Viktor Plahte, born in 1911, who died as an Allied pilot during the Second World War.
He was a board member of Egeberg Brug, Skedsmo Dampsag og Høvleri, Nydalens Compagnie, Meråker Brug and Norsk Skibs-Hypothekbank. He chaired the supervisory council member of Forsikringsaktieselskabet Norden and was a supervisory council member of Filharmonisk Selskap. He was a member of the gentlemen"s club Saskatchewan Fram since 1902, and was proclaimed lifetime member in 1964.
