In 1967, he opened his own firm, Warren Platner Associates, in New Haven, CT. Platner's architectural pursuits include the Georg Jensen Design Center and the Windows on the World restaurant in the original World Trade Center, but, today Platner is best known for his furniture design.

His first and most famous collection produced by Knoll in 1966 was the Platner Collection, which contained tables and seating that attempted to merge modernism with "the kind of decorative, gentle, graceful kind of design that appeared in period style like Louis XV." He invented the production techniques for the collection, with each chair requiring over a thousand welds and more than one hundred cylindrical steel rods.