Nat rose to become a politician (7)
I believe the answer is:
senator
'a politician' is the definition.
(senator is a kind of politician)
'nat rose to become' is the wordplay.
'to become' is an anagram indicator.
'nat'+'rose'='natrose'
'natrose' anagrammed gives 'SENATOR'.
(Other definitions for senator that I've seen before include "Roman legislator" , "US/Roman politician" , "Member of upper house of legislature" , "US representative" , "Treason committed by member of Upper House" .)