He left classroom education in 1990 to develop software to support teachers, and to promote physics through the writing of textbooks and associated materials.

In 1990 he left this post to pursue his career as a full-time author of physics textbooks.

Johnson has written or co-written over 100 books[1][2][3][4] that have attracted many reviews in independent journals[5][6][7] and are referred to in official UK syllabuses and qualifications.

[6][10][11] Johnson has developed software to support teachers in Secondary Schools in the UK and across the world,[12] including TimeTabler[13] which is a program to help timetablers to schedule their school timetables, Options,[14][15] StaffCover[16] and Lesson Loader.

[33] He has written about the French Pyrenees[34] and contributed to the book 'Corsavy – Paysages & Visages'.