The new DUP leader says Northern Ireland risks losing out on economic opportunities because of the Brexit border in the Irish Sea.
In his first television interview since taking up the post, Sir Jeffrey Donaldson told Sky News the prime minister needs to restore Northern Ireland's place in the UK, both economically and constitutionally.
The Northern Ireland Protocol, agreed between the UK and EU, established a trade border in the Irish Sea to avoid any need for a border on the island of Ireland.
Sir Jeffrey said: "I believe there are opportunities going forward but we can't get to those opportunities because of these unnecessary barriers.
"Much of our supply chain comes from Great Britain, whether you are a consumer buying goods in the supermarket or a business relying on component parts for your manufacturing process.
"We need to fix that supply chain problem, we need to restore Northern Ireland's place within the UK, both the market and constitutionally.
"If we can do that then, yes, we will see the opportunities that will flow, providing we can find practical solutions on trade with the EU," he added.
With the DUP under pressure from loyalists protesting about the Irish Sea border, he said the removal of the Protocol is the only path to stable devolved government.
The Lagan Valley MP, who is expected to quit Westminster to become First Minister in Northern Ireland, is also calling for a process to address the legacy of The Troubles.
On Friday, another two historical prosecutions collapsed in Northern Ireland, including that of 'Soldier F' who had been charged with the murders of two men on Bloody Sunday in 1972.
Sir Jeffrey said: "I think we need a process that moves us from where we are to where we can finally say well look, we've examined the past, we have given people the opportunity to explore whether there is the prospect of prosecutions against those who murdered their loved ones and then yes, we need to move to the next phase of the peace process.
"We need some form of process that recognises the suffering of many, the injustice that many feel in Northern Ireland. I don't think you can pull a veil over that."