The American 400 metres runner Shana Cox will represent Britain from November after the IAAF approved her switch of nationalities.
Cox, 26, could compete for her adopted country at the 2012 Olympics in London, where both her parents were born.
The New York-born athlete has a personal best of 50.84 seconds. Only three active British athletes, including Olympic champion Christine Ohuruogu, have run quicker over 400m.
Cox said: "This is something I've always wanted, and I'm looking forward to being part of an amazing team."
Tiffany Ofili, a US-born sprint hurdler, and Anguilla-born long-jumper Shara Proctor have recently switched allegiances to Britain.Reuse content