A Downing Street spokesperson said the prime minister had pressed the US president over the phone to send Anne Sacoolas – who is accused of killing Harry Dunn by dangerous driving last year – to face justice in British courts after an extradition request was denied.
The two countries have been locked in a diplomatic row after Ms Sacoolas, a US citizen, claimed diplomatic immunity and flew home following the crash.
The US said earlier this week that it would not comply with an extradition request.
Dominic Raab, the British foreign secretary, called the refusal a ”denial of justice”.
A Downing Street spokesperson said Mr Johnson “raised the tragic case of Harry Dunn” during a phone call with Mr Trump on Friday, emphasising “the need to secure justice for Harry‘s family”.
“He reiterated the need for the individual involved to return to the UK,” the spokesperson said.
Ms Sacoolas, who is reportedly the wife of an American intelligence official, is accused of killing Mr Dunn by driving into his motorbike near RAF Croughton in Northamptonshire last August.
Mr Dunn’s parents have been campaigning for the suspect to face trial in the UK, where she was charged with causing death by dangerous driving towards the end of last year.
A spokesman for the US State Department said the extradition request, which Washington has called “highly inappropriate”, was rejected because it threatened the entire premise of diplomatic immunity and set a troubling precedent.
Mr Raab said he has spoken to the US ambassador to “express the government’s disappointment about this decision”, adding: “The UK would have acted differently if this had been a UK diplomat serving in the US.”
Ms Sacoolas’s claim to diplomatic immunity has been disputed since the crash, with the Foreign Office saying in October that it is “no longer relevant” to the case. She was subsequently charged by the Crown Prosecution Office.
Mr Dunn’s parents have since asked the UN to review rules surrounding diplomatic immunity, which they have claimed are “outdated” and “abused frequently”.
Additional reporting by Press Association