Hamish Vernal had been a member of the SNP since the age of 16, but now, at 76, he said joining and supporting Alba was a “pragmatic decision”, the Evening Express reports.
Mr Vernal is no longer a serving councillor, but after three currently serving elected members of Aberdeenshire Council formed an official Alba Party group on Sunday, the former Provost announced his political decision.
Councillors Leigh Wilson, Alastair Bews and Brian Topping have all joined Alba having previously been elected as SNP councillors.
Mr Vernal told the Evening Express: “With Alex Salmond heading up the Alba candidates for the North-East, I am delighted to be giving my support to Alba on the second vote for the regional list.“I have been an SNP member since I was 16 years old, so it is a considerable wrench to leave the party.
“However, the opportunity to build a supermajority for independence is too good to miss.”
Alex Salmond will set out his new party’s “route to independence” on Tuesday, the former first minister has said.
In an address scheduled for Tuesday afternoon, the Alba Party leader will make what he called the “declaration for Scotland”, on the anniversary of the Declaration of Arbroath.
Mr Salmond said on Monday that momentum was with the Alba Party, which claimed on Friday to have signed up more members than the Scottish Lib Dems in the seven days from its launch.