He was Reader in Medieval German Literature at the University of Cambridge and a fellow of Pembroke College.

[2] He was awarded a BA in French and German from King's College, Durham (now the University of Newcastle Upon Tyne) in 1951, and his Dr.Phil.

[5] His interest in and support for younger linguists was reflected in school visits and A-level examining.

[8] Johnson's magnum opus, Die Höfische Literatur der Blütezeit: (1160/70-1220/30) (1999), is considered the authoritative work on that subject.

A festschrift in Johnson's honor, Blütezeit (2000), was published by Max Niemeyer Verlag in 2000, and reprinted by Walter de Gruyter in 2012.