He studied architecture at the Norwegian Institute of Technology (Norges tekniske høgskole) until 1935.

During the occupation of Norway by Nazi Germany Viksjø was imprisoned in Grini concentration camp from April 1944 to the war's end in May 1945.

He earned the architecture and civil engineering award Betongtavlen in 1961 for Bakkehaugen Church and 1963 for Tromsø Bridge.

In 1950, he was co-inventor (together with civil engineer Sverre Jystad) of this method of casting and machining concrete to achieve special surface effects in facades.

A number of Viksjø designed buildings are listed with natural concrete including the high-rise government block in Oslo (Regjeringskvartalet), Bergen City Hall (Bergen rådhus) as well as headquarter buildings of Norsk Hydro in Bygdøy and Standard Telefon og Kabelfabrik.