His Excellency advanced and was first to be cured (6)
I believe the answer is:
healed
'be cured' is the definition.
(I've seen this in another clue)
'his excellency advanced and was first' is the wordplay.
'his excellency' becomes 'he'.
'advanced' becomes 'a' (abbreviation).
'and' means one lot of letters go next to another.
'was first' becomes 'led' (to lead is to go first).
'he'+'a'+'led'='HEALED'
'to' acts as a link.
(Other definitions for healed that I've seen before include "Made well" , "Put right" , "Cured, mended" , "Became healthy again" , "Mended, recovered" .)