Performers ready to model with painter’s backing (8)
I believe the answer is:
artistes
'performers' is the definition.
(artiste is a kind of performer)
'ready to model with painter's backing' is the wordplay.
'ready to' becomes 'set' (synonyms).
'model' becomes 'sit' (e.g. for a painting).
'with' means one lot of letters go next to another.
'painter' becomes 'RA' (member of the Royal Academy of Arts).
'backing' says the letters should be written in reverse.
'set'+'sit'+'ra'='setsitra'
'setsitra' back-to-front is 'ARTISTES'.
(Other definitions for artistes that I've seen before include "Professional entertainers, singers or dancers" , "Public performers" .)