Writer has done paralegal nonsense (5,5,3)
I believe the answer is:
edgar allan poe
'writer' is the definition.
(American writer)
'done paralegal nonsense' is the wordplay.
'nonsense' indicates anagramming the letters.
'done'+'paralegal'='doneparalegal'
'doneparalegal' with letters rearranged gives 'EDGAR ALLAN POE'.
'has' acts as a link.
(Other definitions for edgar allan poe that I've seen before include "Writer producing horror" , "... American poet and mystery writer" , "Poet and writer of the macabre" , "US" , "Short-story writer" .)