Leader prior to restoration of emir (7)
I believe the answer is:
premier
'leader' is the definition.
(premier is a kind of leader)
'prior to restoration of emir' is the wordplay.
'prior to' becomes 'pre' (I've seen this in another clue).
'restoration of' indicates anagramming the letters (the order of letters restored or reset).
'emir' anagrammed gives 'mier'.
'pre'+'mier'='PREMIER'
(Other definitions for premier that I've seen before include "Prime minister" , "Aberdeen or Salisbury?" , "First - head of government" , "Foremost" , "PM" .)