Agent put up by one-time artiste (9)
I believe the answer is:
performer
'artiste' is the definition.
(I've seen this before)
'agent put up by one-time' is the wordplay.
'agent' becomes 'rep' (short for representative).
'put up' says the letters should be written backwards.
'by' is a charade indicator (letters next to each other).
'one-time' becomes 'former' (I've seen this before).
'rep' written backwards gives 'per'.
'per'+'former'='PERFORMER'
(Other definitions for performer that I've seen before include "Fred Astaire, say" , "Such as a musician or actor" , "player" , "artist" , "Eg 9 [ACTRESS]" .)