US resident Anne Sacoolas will be charged with death by dangerous driving after the death of motorcyclist Harry Dunn, 19. It is believed Mrs Sacoolas was driving on the wrong side of the road as she left the RAF base, colliding with and killing Mr Dunn.
Mr Dunn died after his motorbike was in collision with a car owned by Mrs Sacoolas outside RAF Croughton where her husband Jonathan worked as an intelligence officer. Mrs Sacoolas, 42, left the UK and returned to her native US, claiming diplomatic immunity.
The Crown Prosecution Service (CPS) said it had started extradition proceedings through the Home Office.
Lawyer Amy Jefress said: "Anne will not return voluntarily to the UK to face a potential jail sentence for what was a terrible but unintentional accident."
Mr Dunn's mother Charlotte Charles said the family was "relieved" Mrs Sacoolas had "finally" been charged.
Speaking outside the CPS headquarters she said: "We feel that we have made a huge step in the start of achieving the promise to Harry that we made.
"We made that promise to him the night we lost him to seek justice thinking it was going to be really easy.
"We had no idea it was going to be so hard and it would take so long."