He was the son of the hardware dealer and cinema owner Carl Otto Severin Gladtvet (1863–1918) and Agnes Elisabet Roshauw (1862–?).
The first feature film was the western-inspired Overfaldet paa postaapnerens datter eller Kampen om pengebrevet from 1913.
Gladtvet was only partly involved in the pioneering days of Norwegian cinema, and he sometimes acted as Peter Lykke-Seest's photographer.
In 1939, Ottar Gladtvet made a full-length documentary film that documented the Norwegian royal couple on their journey to the United States: Til Vesterheimen (To Vesterheim).
It chronologically follows the royal couple's journey through the country as they meet many famous people, such as Franklin D. Roosevelt, Sonja Henie, and Henry Ford.