Khalaf Ali, 45, a second secretary at his embassy, was shot at night on March 6, near the embassy in the capital's posh diplomatic zone. Ali was the head of Saudi citizen affairs at the embassy.
"The convicts will be hanged by neck till their death," Speedy Trial Tribunal-4 Judge Mohammad Motahar Hossain said while pronouncing the verdict in a packed courtroom.
While four convicts Saiful Islam Mamun, Al Amin, Akbar Ali, Rafiqul Islamand were arrested by police in July, the fifth accused Selim Chowdhury is absconding.
The judge said the punishment of the fugitive convict would be effective from the day of his arrest or surrender, the court said.
Immediately after the verdict police whisked the convicts off to the high security Dhaka Central Jail, where they would await subsequent legal procedures to be executed.
Saudi ambassador in Dhaka Abdullah Bin Naser Al-Busairi a brother of the victim was present at the court.
Bangladesh police said the four confessed their involvement in the killing during the interrogation, while "it appeared to be an unplanned murder and case of simple mugging."
Al Amin made a confessional statement at the CMM court on September 20. He said he, along with four others, were present during the murder, when an accused Saiful shot Khalaf.
The judgement came two months after the court indicted the five suspected murderers as Dhaka had assured Riyadh of trying the assailants through a fast track tribunal.
Saudi Arabia had earlier sent a fact finding delegation in Bangladesh as no apparent headway could be made in the investigation for months, but the Saudi envoy recently said his government was happy with the arrest of Ali's suspected killers and Dhaka's assurance of trying the killers in quickest possible time.
Saudi Arabia is a top destination for migrant workers from Muslim-majority Bangladesh while the two countries enjoy good relations which, however, were tested last October, when Saudi Arabia beheaded eight Bangladeshi workers who were found guilty of robbing and killing an Egyptian.