Former Ulster Unionist David McNarry had a stark message for his old party as he formally announced his decision to join the UK Independence Party.
He said: "I am a politician, I am a professional politician and as far as I am concerned I am on the way up.
"I am not associated with anybody or anything that's in decline, and you best understand that. I'm on the way up."
Mr McNarry said any of his former colleagues in the UUP would be welcome in UKIP if they decided to jump ship.
He said: "I have not defected from anyone. I have willingly joined. The choice was mine."
UKIP leader Nigel Farage was at Parliament Buildings in Stormont with Mr McNarry to welcome the party's first Assembly Member into its ranks.
He said the development was proof that UKIP was a "truly, genuinely national" party, accusing other political parties of ignoring Northern Ireland.
Mr Farage said UKIP had big plans for Northern Ireland and confirmed the party would stand in European elections in 2014.
Mr McNarry, 64, fell out with the leadership of the Ulster Unionists in January after giving an interview in which he talked up the prospect of the UUP joining forces with its main rival, the Democratic Unionist Party.
Disciplinary action by then-leader Tom Elliott prompted the MLA to resign from the party's Assembly grouping.
He was subsequently expelled from the party outright.
