Happen to get hold of seat (4,5)
I believe the answer is:
take place
'happen' is the definition.
(synonyms)
'get hold of seat' is the wordplay.
'get hold of' becomes 'take' (taking is a kind of getting hold of).
'seat' becomes 'place' (synonyms).
'take'+'place'='TAKE PLACE'
'to' is the link.
(Other definitions for take place that I've seen before include "Talk peace (anag) - happen" , "Occur, happen - assume position" .)