Stimulate a Svengali into action (9)
I believe the answer is:
galvanise
'stimulate' is the definition.
('stimulate'->'galvanize' is in my internal thesaurus and 'ize'->'ise')
'a svengali into action' is the wordplay.
'into action' indicates an anagram (letters become active or mobile).
'a'+'svengali'='asvengali'
'asvengali' is an anagram of 'GALVANISE'.
(Other definitions for galvanise that I've seen before include "Excite" , "Electrify" , "subject to action of electric current" .)