Police originally charged the two migrant workers with the murder of David Miller, 24, and the rape and murder of Hannah Witheridge, 23, in October, citing DNA tests and later confessions by the pair to the crime on the diving island of Koh Tao.
But Zaw Lin and Win Zaw Tun, both in their 20s, later retracted their confessions, alleging they were obtained under duress, raising concerns over the probity of the investigation.
But today they agreed to finally indict the suspects for trial.
"They (the two suspects) were charged with intentional murder," Paiboon Archavanuntakun, Koh Samui's chief prosecutor, told AFP.
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"Tomorrow afternoon (Thursday), the order will be submitted to the Koh Samui provincial court," he said.
"There will then be a trial," he added, without giving details of a timeframe.
The start of court proceedings will come as a blow to the men and their families, who have made impassioned appeals in Myanmar and Thailand for their release.
The murders, which occurred in September on a normally tranquil island, also cast a long shadow over the nation's reputation as a tourist haven, prompting the Thai junta leader Prayut Chan-O-Cha to vow to swiftly bring the killers to justice.
Alarmed by the initial handling of the probe -- which saw reporters allowed to trample all over the crime scene among a slew of apparent bungles -- a team of British detectives visited Thailand in November to review the investigation.