Party welcomes Northern Ireland outlaw (6)
I believe the answer is:
banish
'outlaw' is the definition.
(I've seen this before)
'party welcomes northern ireland' is the wordplay.
'party' becomes 'bash' (term for a party or celebration).
'welcomes' indicates putting letters inside (in sense of 'invites in').
'northern ireland' becomes 'NI' (abbreviation).
'bash' going around 'ni' is 'BANISH'.
(Other definitions for banish that I've seen before include "dislodge" , "Deport, exile" , "Send into exile" , "Cast out, ostracize" , "Drive away, maybe from country" .)