Woody Johnson said Trump was "more than capable" of dealing with any "discord" he may face when he finally visits later this year.
"This president is not worried about protests," Johnson told ITV television.
"In the US, here, anywhere. He is very, very certain of where he wants to take the country and he's more than happy to deal with the different views and express his own view.
"The president is more than capable of handling any sort of discord."
Trump met British Prime Minister Theresa May at the World Economic Forum in Switzerland last week and they agreed that he would make his long-planned trip to Britain later this year.
A year ago, May proposed that Trump make a state visit to Britain, but there was speculation it would be cancelled due to strong public and political opposition to the president in the UK.
A senior British government source was unable to say whether Trump would receive the prestigious welcome initially offered, or whether his trip would be scaled down to a working visit.
Johnson said: "What the British people should look for is actually what he's accomplished and where he wants to go."
He admitted that Trump's relationship with the media had been "terrible in one way but he is getting the message out in his own unique way".
Johnson said he thought Trump would "absolutely" be a two-term president.
"If the president decides to run, he'll win... I think he'll decide to run," he said.
