Sir Reg Empey said it was time for unionism to start afresh
The two main unionist parties need to review their entire approach to working together, Sir Reg Empey has said.
The UUP leader is to step down in the autumn and he has suggested DUP leader Peter Robinson should do the same.
DUP MP Sammy Wilson said his remarks about Mr Robinson were a "desperate attempt to deflect attention from the UUP's internal splits and divisions".
Sir Reg told the BBC's Politics Show on Sunday it was time for some long-term thinking within unionism.
He said unionist unity candidate Rodney Connor's failure to capture the Fermanagh and South Tyrone seat from Sinn Fein showed that "bolting the parties together" did not work.
"There is an opportunity now to have a fairly clean slate - with a new leadership - to look forward to the next decade because we're going to have to think as unionists long-term, not short-term," he said.
"Republicans look at it in terms of generations and I think we've got to start looking at it the same way."
Sir Reg suggested on Saturday that Mr Robinson should also step aside, having lost his East Belfast Westminster seat to the Alliance Party.
However, Mr Wilson said on Sunday that Sir Reg's UUP strategy was widely rejected "while Peter Robinson's DUP strategy, vision and policies were endorsed across Northern Ireland".
"Given that the UUP is in such a shambolic position with splits and divisions on the front pages of our papers on a daily basis, Reg would be better to concentrate on his own problems rather than trying to tell other parties how to operate," he said.
A new Ulster Unionist leader is expected to be in place ahead of its party conference in late October or early November.
Its 100-strong party executive met on Saturday after its electoral pact with the Conservatives failed to secure any Westminster seats.
It is believed party colleagues had urged him to stay on but Sir Reg said it was the right time for him to quit.
The UUP has also decided to hold a "forensic" review of its relationships with other political parties, including the Conservatives and the DUP.