He went on to work with legendary architects Raymond Loewy, Eero Saarinen, and I. M. Pei before opening his own architecture practice. Platner made notable architectural contributions throughout his career, including the Georg Jensen Design Center and the Windows on the World restaurant in the World Trade Center, both in New York City.

It was his furniture collection for Knoll, however, that earned Platner worldwide renown. Originally introduced by Knoll in 1966, the Platner Collection is an icon of modern furniture. Platner personally formulated the production techniques for the complicated designs with each chair requiring over a thousand welds and more than one hundred cylindrical steel rods. Knoll also introduced an executive private office collection designed by Platner.