In an emailed statement, Kim Darroch resigned, saying the "current situation is making it impossible for me to carry out my role as I would like."
Here's the full text of his resignation letter:
Since the leak of official documents from this embassy there has been a great deal of speculation surrounding my position and the duration of my remaining term as ambassador. I want to put an end to that speculation. The current situation is making it impossible for me to carry out my role as I would like.
Although my posting is not due to end until the end of this year, I believe in the current circumstances the responsible course is to allow the appointment of a new ambassador.
I am grateful to all those in the UK and the US, who have offered their support during this difficult few days. This has brought home to me the depth of friendship and close ties between our two countries. I have been deeply touched.
I am also grateful to all those with whom I have worked over the last four decades, particularly my team here in the US. The professionalism and integrity of the British civil service is the envy of the world. I will leave it full of confidence that its values remain in safe hands.
In a response to Darroch's letter, the head of the UK diplomatic service praised Darroch for doing his job with great dignity "as you always have" and blamed a "malicious leak" for undermining him.