Louis Susman told the Commons Foreign Affairs Committee it was “fair and balanced” and “promotes the interests of justice” in both countries.
His comments follow high-profile cases, including that of Gary McKinnon, the alleged hacker who has been fighting extradition to the US for years.
The meeting came ahead of a Commons debate on the controversial issue.
In unusually strong language for a diplomat, the ambassador attacked those who believe the treaty is biased in favour of the US.
“The constant use of skewed arguments and wilful distortion of the facts by some to advance their own agendas remains of great concern to the United States,” he said.
“It would be wrong to view the extradition treaty through the prism of individual cases where sentiment and emotion can cloud reality and lead to misrepresentation.”
The treaty was being “widely and wrongly condemned” by “some in parliament and in sections of the British media”, he said.
An independent review of the treaty led by the former Court of Appeal judge Sir Scott Baker found it “does not operate in an unbalanced manner”, he added.
Louis Susman said: “I believe that having signed the treaty, and having had it tested both through the British justice system and by independent experts, it is now incumbent on the UK government to stand in support of it.”
The review “reached the only conclusion that could be supported by the facts: that the US-UK treaty is balanced, fair, and needs no changes”.
Opponents of the treaty argue it is unfair for the United States to require “sufficient evidence to establish probable cause” before agreeing to extradite anyone to Britain, while Britons are denied the same protection.
Nine cases, including those of Abu Hamza and Babar Ahmed, are still awaiting rulings, including two which involve allegations dating back to 1997.
Parliament’s Joint Committee on Human Rights criticised those delays.
“Delays of this kind are, in our view, unacceptable; they are unfair to the individual and militate against the prospects of a fair trial,” the report said.
Figures released in the report show between January 2004 and July 2011, there were 130 requests by the US for people to be extradited from the UK, compared with 54 requests from the UK to the US.
But Louis Susman says it is not the case, as some claim, that it is easier to extradite someone from the UK than from the US.
“The United States has never denied an extradition request from the UK. under the treaty,” he said.
“The UK has refused on seven occasions.
“Second, the standard that each country has to meet to extradite someone is the same.
“I would like to repeat that: the standard is the same.”
UK-US extradition will be debated in the Commons on Monday.
The backbench debate – put forward by 45 MPs – calls on the treaty to be “urgently renegotiated” to enable the government to refuse extradition requests if UK prosecutors have decided against beginning proceedings at home.