Leading empire corrupted Republican (7)
I believe the answer is:
premier
'leading' is the definition.
(premier can mean leading or important)
'empire corrupted republican' is the wordplay.
'corrupted' is an anagram indicator.
'republican' becomes 'r' (abbreviation).
'empire' is an anagram of 'premie'.
'premie'+'r'='PREMIER'
(Other definitions for premier that I've seen before include "Chief minister" , "Earliest" , "Aberdeen or Salisbury?" , "First (minister)" , "Leading" .)