Swain, from Jamestown, Rhode Island, was convicted on 27 October in a British-law Virgin Islands court of murdering Shelley Tyre.
The jury accepted prosecution evidence that Swain had held her from behind and had turned off her air supply until she succumbed.
Sentencing yesterday, Justice Indra Hariprashad-Charles said: "It is my view that this murder was carefully planned and premeditated and calls for stiff punishment."
The judge added that, due to the crime’s premeditated nature, she was bound to deny a request from Swain’s defence that he should be eligible for parole once he had served 18 years in prison.
Swain will serve his sentence in HM Prison at Balsam Ghut on Tortola.
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