Celebrate one included in duty list (7)
I believe the answer is:
roister
'celebrate' is the definition.
(I know that roister is a more specific form of jollify)
'one included in duty list' is the wordplay.
'one' becomes 'i' (Roman numeral).
'included in' is an insertion indicator.
'duty list' becomes 'roster' (I've seen this before).
'i' put inside 'roster' is 'ROISTER'.
(Other definitions for roister that I've seen before include "Rioters (anag.)" , "Carouse" , "riot" , "bluster" , "Revel noisily, swagger" .)