Fellow's thus held to be a craftsman (5)
I believe the answer is:
mason
'a craftsman' is the definition.
(mason is a kind of craftsman)
'fellow's thus held' is the wordplay.
'fellow' becomes 'man' (I've seen this before).
'thus' becomes 'so' ('so' can be a synonym of 'thus').
'held' indicates putting letters inside.
'man' placed around 'so' is 'MASON'.
'to be' is the link.
(Other definitions for mason that I've seen before include "member of charitable society" , "Stone carver" , "figure in lodge" , "Construction industry employee" , "Stone-carver" .)