The Home Office has said it has submitted an extradition request for the suspect charged in connection with the death of teenage motorcyclist Harry Dunn.
Anne Sacoolas was charged with causing the 19-year-old's death by dangerous driving last month.
Harry died after his motorbike crashed into a car outside RAF Croughton in Northamptonshire on August 27 last year.
The 42-year-old suspect, the wife of a US intelligence official, claimed diplomatic immunity after the collision and was able to return to her home country, sparking an international controversy.
Now, the Home Office has said the matter is now "a decision for the US authorities" after formally submitting the extradition request on Friday.
Confirming the extradition request, a spokesman for the Home Office said: "Following the Crown Prosecution Service's charging decision, the Home Office has sent an extradition request to the United States for Anne Sacoolas on charges of causing death by dangerous driving.
"This is now a decision for the US authorities."
Harry's family have said they are "pleased" with the development, adding that they feel it is a "huge step towards achieving justice for Harry".
The family have initiated various legal proceedings against the Foreign Office, the US government and Mrs Sacoolas herself after their lawyers disputed the granting of diplomatic immunity.
Reacting to the extradition request, spokesman Radd Seiger told ITV Anglia it's a 'is a giant stride forward' for the family.
"This is clearly a huge step towards fulfilling the promise they made to their son as he was dying in hospital, that they would not rest until they got him justice.
"Everyday is a battle and they wake up with that feeling in the pit of their stomach that Harry is no longer here."