A senatorship arranged for classical writer (12)
I believe the answer is:
aristophanes
'for classical writer' is the definition.
(I've seen this before)
'a senatorship arranged' is the wordplay.
'arranged' is an anagram indicator.
'senatorship' with letters rearranged gives 'ristophanes'.
'a'+'ristophanes'='ARISTOPHANES'
(Other definitions for aristophanes that I've seen before include "Classical writer" , "Playwright" , "Greek comic dramatist - writer of Lysistrata, d. about 385 BC" , "Ancient Greek dramatist" , "Old dramatist" .)