Admittedly garrulous leader went on and on (7)
I believe the answer is:
granted
'admittedly' is the definition.
(I've seen this before)
'garrulous leader went on and on' is the wordplay.
'leader' indicates taking the first letters.
'went on and on' becomes 'ranted' (I've seen this in another clue).
The first letter of 'garrulous' is 'g'.
'g'+'ranted'='GRANTED'
(Other definitions for granted that I've seen before include "One doesn't like being taken for it" , "Given; allowed" , "Admittedly; given" , "Admittedly; gave formally" , "Conceded" .)