Born in New York City in 1916, Johnsen received a master's degree in architecture from the Harvard Graduate School of Design in 1942. He worked under Marcel Breuer and for the National Housing Agency in Washington, D.C., before joining the New York office of Skidmore, Owings & Merrill. Johansen opened his own private office in New Canaan, Connecticut, in 1948. His major projects included the Oklahoma (Mummers) Theater in Oklahoma City, Okla.; the Goddard Library at Clark University in Worcester, Mass.; the L. Frances Smith Elementary School in Columbus, Ohio; Clowes Memorial Hall at Butler University in Indianapolis, Ind.; the Charles Center Theater Building (Mechanic Theater) in Baltimore, Md.; Staten Island Community College in Staten Island, N.Y.; and the United States Embassy in Dublin, Ireland. Johansen also designed numerous private residences in Connecticut and New York state, as well as a series of conceptual projects, including a "Bubble Cluster," a Mag-Lev Theater, and a "Moon Module" house.
Collection includes original and reprographic architectural drawings, photographs, negatives, professional papers, publications, reference files, and one scale model.