Senator Cory Bernardi says his fledgling Australian Conservative's party will fight on after the defection of its lone South Australian MP to the Liberals.
Upper house member Dennis Hood jumped ship on Monday after first discussing the possible move with the new Liberal government last week.
Mr Hood denied his decision was motivated by self-interest.
He said it was prompted by his support for the government's vision for SA and the poor performance of the Australian Conservatives at the recent state election.
"They received just over three per cent of the first preference votes in the lower house which is not going to get anyone anywhere," he said.
"If you want to stay with something that's heading down that path, then pretty soon you'll find that they have no members of parliament and really no impact."
But the Australian Conservatives' founder said Mr Hood's decision was disappointing and maintained his party had a future.
"It was a shock to me this morning, but it is taken, in light, I guess of Dennis' own future career prospects," Senator Bernardi said.
"When I started this party, it was about putting principles ahead of personalities, it was about putting policy ahead of politics and that is more important than ever.
"The reality is we have just had an election and we haven't had the result we wanted to achieve, and I guess Dennis thought he could achieve the results he wants by joining the Liberal party."
Mr Hood was elected to parliament's upper house in 2006 as a Family First MP, but joined Senator Bernardi's group last along with fellow Family First upper house MP Rob Brokenshire.
He conceded on Monday that was probably not a wise move.
While final preferences are still to be distributed, Mr Brokenshire is unlikely to be returned after the Australian Conservatives attracted just 3.5 per cent of the Legislative Council vote.
New Premier Steven Marshall said Mr Hood would bring great experience to the Liberal line-up.
"He's a diligent, hard-working, highly capable member," Mr Marshall said.
"It's great news for the Liberal Party but most importantly it's great news for the parliament and the people of South Australia."
