The former London Mayor faced claims he hadn’t offered enough support for Sir Darroch, who resigned from his position as ambassador to Washington after memos of him describing Mr Trump as “inept” were leaked.
Mr Johnson hit back at accusations that he threw Sir Darroch “under the bus” to strengthen his ties with the US President.
He said: “I will stand up for our fantastic diplomats across the world.”
He said he believed Britain’s relationship with the United States was the “single most important strategic fact of our times”.
Mr Johnson added: “I criticised him as foreign secretary.
“We in the UK do not agree with the position of the United States on global warming or their approach to the Iran nuclear deal. We were very robust and will continue to be robust with the US.”
Sir Darroch sensationally resigned yesterday after Mr Trump launched a scathing Twitter attack branding the ambassador as “wacky”.
In his resignation letter he said it had become “impossible” to carry out his £185,000-a-year role after leaked memos revealed he called Mr Trump “inept”, “insecure” and “incompetent”.
In the sensitive documents, Sir Darroch allegedly voiced fears that the American president could also still attack Iran.
He wrote: “We don’t really believe this Administration is going to become substantially more normal; less dysfunctional; less unpredictable; less faction riven; less diplomatically clumsy and inept.”
‘HE IS INEPT’
Mr Trump tweeted on Monday blasting Prime Minister Theresa May while harshly commenting on Sir Darroch.
He said: “I have been very critical about the way the UK and Prime Minister Theresa May handled Brexit.
“What a mess she and her representatives have created.
“I told her how it should be done, but she decided to go another way.
“I do not know the Ambassador, but he is not liked or well thought of within the US. We will no longer deal with him.”
The Tory leadership frontrunners comments tonight were made during a hustings event where he attended with rival Jeremy Hunt.
Mr had previously come out in full support of Sir Darroch.
The Foreign Secretary stood by popular Sir Kim, 65, who previously worked as the PM’s National Security Adviser.
Mr Hunt said he was “doing his job” as “frank opinions” from ambassadors are vital.
But in a bid to smooth over the Transatlantic rift, Mr Hunt added: “It’s also important to say this was a personal view. It’s not the view of the British government. It’s not my view.
“We continue to think that under President Trump the US administration is not just highly effective but the best possible friend of the United Kingdom on the international stage.”
I criticised him as foreign secretary. We in the UK do not agree with the position of the United States on global warming or their approach to the Iran nuclear deal. We were very robust and will continue to be robust with the US.