The Chonburi Provincial Court sentenced 25-year-old Anuchit Lamlert for killing Tatiana Tsimfer, 30, and Liubov Svirkova, 25, on Feb. 24, said the official, speaking on condition of anonymity because he is not its spokesman.
Their bodies were found shot and slumped in lounge chairs on a beach.
Anuchit has testified that the motive for the killings was robbery and that he killed the pair because they started crying out for help and he was afraid they would remember his face after they saw him.
He was charged for premeditated murder, robbery, consumption of methamphetamine, and illegal possession and usage of weapons.
Anuchit's father, Suchart, said that he would appeal the court's verdict.
The victims were on a package tour and had flown to Thailand on a chartered flight. Pattaya, about 110 kilometers (70 miles) southeast of Bangkok, is particularly popular with Russian tourists.
Pattaya is known for its beaches, thriving sex industry and high crime rate.