He, a stoic, a smashing prime minister (9)
I believe the answer is:
taoiseach
'prime minister' is the definition.
(term for the Irish prime minister)
'he a stoic a smashing' is the wordplay.
'smashing' is an anagram indicator.
'he'+'a'+'stoic'+'a'='heastoica'
'heastoica' with letters rearranged gives 'TAOISEACH'.
(Other definitions for taoiseach that I've seen before include "Irish PM" , "PM in Dublin" , "Irish premier" , "Leader of the government" , "Western PM" .)