Stephen Moore, senior economic adviser to Mr Trump, said the centrepiece plan of the new administration was wooing back multinationals with radical business tax cuts.
“I believe that when we cut these tax rates — we’re going to cut our business tax rate from roughly 35% down to roughly 15% to 20% — if you do that you are going to see a flood of companies leaving Ireland and Canada and Germany and France and they are going to come back to the United States,” he said.
“It is going to have a very high impact on jobs.”
Mr Moore, formerly a chief economist with US conservative think-tank the Heritage Foundation, said the effort to entice companies back from low corporate tax-rate countries would be central to boosting the US economy.
This was the “single most important thing for our country right now”, he told BBC Radio 4’s World At One.
“There is no question about it, and we see day after day in this country that we are losing our businesses and our corporations,” he said.
“They are effectively renouncing their US citizenship and they are moving to Canada, to Britain, to Ireland, to China and Mexico. That is a significant loss of jobs and we want to have the jobs here in the United States, we don’t want to have them go abroad.”
The remarks follow a 10-minute telephone conversation on Wednesday night between Mr Trump and Taoiseach Enda Kenny, who said the president-elect praised his economic policy.
“I had a very good conversation with the president-elect,” said the Taoiseach.
“He understands Ireland very well, he was complimentary about the decisions made about the economy here.
“He is looking forward to doing business with Ireland and I asked him specifically about (St) Patrick’s Day, he is looking forward to continuing that tradition over many years.”
It is tradition for the Taoiseach to travel to Washington on March 17 to present the US president with a bowl of shamrocks, to symbolise close ties between the countries.
Mr Kenny said Mr Trump has invited him to the White House next year to continue the custom.
Earlier on Wednesday, Mr Kenny told the Dáil that “racist and dangerous” remarks made by Mr Trump during the election campaign were made in the “heat of battle”.
In a softening of his outspoken rebuke from May, Mr Kenny said he would be happy to work with Mr Trump.
Weeks after making the comments, when asked if he would put that view to the then presidential hopeful in any future meeting, Mr Kenny said: “Certainly. I’d be very happy to.”
But pressed again in the Dáil hours after the US election result was announced, Mr Kenny appeared to relax his stance.
“I’d be happy to deal with the president in a very constructive way as he has announced to the world that his administration will work to heal the wounds in America, will work to have the American people unite and form partnerships with like-minded countries,” he said.