Mrs Ann Ingram's decision to fly to America comes after the Prime Minister sent her a handwritten letter explaining there are "no proper grounds" for him to intervene after she had begged him to help.
Cambridge-born Ingram, 31, the son of an American father, was convicted in 1983 of murdering a neighbour during a burglary while he was drunk and on drugs.
He has been on Death Row in Jackson, Georgia, after a court rejected the pleas of his US lawyer, British-born Clive Stafford-Smith.
In a letter to Mr Major last week, the convicted man's mother said: "It makes me cry every time I think about it, that the State of Georgia wants to put my Nicky in a chair and roast him with 2,000 volts of electricity. I am British, my son is British, with nowhere else to turn. I have to beg you to help save my son's life now."
Mr Major, who begins his three-day visit to Washington today, wrote that: "I found your letter very moving and I can imagine the profound distress you must be feeling". Although he understood her determination to do all she could to save her son, Mr Major concluded "with deepest regret" that there were no proper grounds for the British Government to intervene.
Ingram's only hope is if his lawyers can win an 11th-hour reprieve from the Georgia Board of Paroles and Pardons on Wednesday. They will argue that Ingram has suffered enough by being left on Death Row for 12 years in conditions described as "degrading and inhuman".Reuse content