Johnsson started his career at ABB in Sweden and moved on to UCLA, Caltech, Yale University, Harvard University, the Royal Institute of Technology (KTH in Sweden), and Thinking Machines Corporation.
Johnsson's professional path involved a series of transitions between different organizations, starting with ABB in Sweden and then moving on to prestigious institutions like UCLA, Caltech, Yale University, Harvard University, the Royal Institute of Technology (KTH in Sweden), and Thinking Machines Corporation.