Richard Grenell, who was appointed by President Donald Trump last year, made the highly unusual comments for a diplomat to right-wing Breitbart News.
“I think there is a groundswell of conservative policies that are taking hold because of the failed policies of the left,” he said.
Mr Grenell’s comments follow several other controversial remarks by Trump-appointed diplomats.
In the interview, the ambassador, who only took office last month, said President Trump’s election had energised people to take on the “political class”. Mr Grenell said he had been contacted by people throughout Europe about a conservative “resurgence”.
He attacked the perceived bias of the media and politicians against Mr Trump as “the group-think of a very small elitist crowd”, and praised Austria’s conservative Chancellor Sebastian Kurz as a “rock star”.
Mr Kurz’s party formed a coalition with the far-right Freedom Party in 2017.
Right-wing populists have won support across Europe, with recent electoral success for parties in Italy and Slovenia that espouse strict immigration policies.
Democratic Senator Chris Murphy described the interview as “awful”.
In a tweet, he said he had previously spoken to Mr Grenell about “politicising this post”.
But only an hour after he officially began his role, Mr Grenell provoked controversy for tweeting that German companies should “wind down operations immediately” in Iran, following Mr Trump’s announcement that the US was pulling out of the Iran nuclear deal.
Mr Grenell’s comments are the most recent case of controversial language from a US diplomat.
The US state department’s guide, Protocol for the Modern Diplomat, states that “each country will be respected uniformly and without bias”, and includes the instruction “that as a guest, one is expected to respect the host’s culture”.
However, former US ambassador to Germany John Kornblum told the BBC there is “no lexicon” for ambassadors.
“There is no such thing as diplomatic language,” he said. “The language diplomats use is attuned to their needs.”
For example, during the negotiations for the Dayton Agreement in 1995, Mr Kornblum says there was “incredibly undiplomatic” language used to criticise heads of government, in particular Serbia.
He also believes that in Europe there is a greater degree of “self-censorship” among diplomats that does not apply anywhere else in the world, saying “Europeans are especially sensitive”.
However, he agrees that President Trump has changed things.
“Mr Trump has taken political language in the US to new depths,” said Mr Kornblum. And he thinks diplomats abroad could be trying to emulate their president.
President Trump has infamously dubbed Mexicans “drug dealers” and “rapists”, reportedly used derogatory language to describe some African countries and claimed knife crime in London had left a hospital there “like a war zone”.