Karl-Erik Ekselius studied under Carl Malmsten during the 1930’s and from 1938 in Germany with professor Fritz Breuhaus, one of the founders of the Bauhaus School. In 1948 Ekselius went on a study trip to the USA where he saw how popular Scandinavian design was starting to become.
Ekselius design became something of a mixture of the strict modernistic style and influence from Wiener Werkstätte combined into what can be called Swedish Modern. Ekselius breakthrough as a furniture designer came at the H55 Exhibition in Helsingborg in year 1955 where he presented chairs, a table and a sofa made by his family company J.O. Carlsson Möbelindustri (later JOC) in Vetlanda. One of the most well-known pieces was the armchair F 139 that later was picked out (together with textiles by Astrid Sampe) for the UN Library (also called the Dag Hammarskjöld library) in New York.
In 1970 Ekselius himself took over JOC and ran the company until 1987. In the 1960’s -70´s the company focused more on furniture for public spaces and offices and Ekselius designed among other the armchair Mondo made with a frame of extruded aluminium and leather upholstery. Mondo was also one of the results from the collaboration between JOC and the company Sapa, one of Europe's largest factories for extruded aluminum located in the same city as JOC.
As an interior architect Ekselius worked on projects as the Columbia University in New York and the New Zeeland-house in London. He also designed furniture for the America Line's cruise ships. Karl-Erik Ekselius passed away in 1998 at the age of 84.