He wrote of French opposition (5)
I believe the answer is:
defoe
'he wrote' is the definition.
(I've seen this before)
'of french opposition' is the wordplay.
'of french' becomes 'de' ('of' in French).
'opposition' becomes 'foe' (I've seen this in another clue).
'de'+'foe'='DEFOE'
(Other definitions for defoe that I've seen before include "pamphleteer and novelist" , "Daniel, author of Robinson Crusoe" , "Author of Robinson Crusoe, d. 1731" , "Author of Moll Flanders, d. 1731" , "Writer of Moll Flanders" .)