The battered bodies of Hannah Witheridge, 23, and Leeds University student David Miller, 24, were discovered on a beach on the idyllic holiday island of Koh Tao on September 15 last year.
Burmese migrants Zaw Lin and Wai Phyo, also known as Win Zaw Htun, initially confessed to the killings but later retracted their statements - claiming they had been tortured by police. They face the death penalty if found guilty.
Three judges are expected to return their verdicts at a court on the island of Koh Samui following more than a year of legal proceedings.
Prosecutors say DNA evidence collected from cigarette butts, a condom and the bodies of the victims, links the two suspects to the killings.
But lawyers representing Lin and Phyo, both 22, say DNA samples from the alleged murder weapon - a garden hoe - does not match that of the two suspects.
The defence team claim the defendants’ confessions “came about involuntarily from torture or abuse that made them fear for their lives” in the context of “systematic abuse” of migrants on Koh Tao.
A re-enactment of the murders in which the suspects were paraded in front of the media was also “staged under threat of violence”, the lawyers added.
Thai police have denied using force during their investigation.
Miss Witheridge, a University of Essex student from Hemsby, Norfolk, and Mr Miller, of Jersey, who had just completed a civil and structural engineering degree at the University of Leeds, met on Koh Tao while staying at the same hotel.
Post-mortem examinations showed that both had suffered severe head wounds. Miss Witheridge had been raped while Mr Miller died after being hit over the head before drowning in the sea.
British police officers travelled to Thailand to help with the investigation into the deaths following a direct appeal from Prime Minister David Cameron to Thailand’s military ruler.
The intervention came after General Prayuth Chan-ocha was forced to apologise for suggesting that foreign visitors to his country’s world-famous beaches might be unsafe wearing bikinis following the murders.
It is not yet clear whether the victims’ families will be present for the verdicts on Christmas Eve. They attended the opening of the trial in July when the family of Mr Miller said they “simply want to see justice done fairly and openly”.
The mothers of the two suspects are expected to attend, according to reports.
The hearing is due to begin at 9am local time (2am UK time).