Speaking at the end of the 159-day trial on Thursday, Judge Zaki Yasin said he found the defence of both the accused to be "unbelievable" as "each of them is blaming the other".
"They failed to raise any reasonable doubt in the prosecution's case," said Zaki. "I sentence both of you to death" by hanging, he said.
Azilah and Sirul Azhar looked emotionless as the verdict was read.
Defence lawyers said they would appeal the ruling.
The high-profile case has generated allegations against top members of the Malaysian government, including Najib Abdul Razak, the country's newly-appointed prime minister.
|Abdul Razak Baginda, centre, was acquitted of abetting the murder of his ex-lover [AFP]
Altantuya was the former lover of Abdul Razak Baginda, a close aide to Najib and a well-known defence analyst.
Najib has firmly denied any links, and the case has not directly implicated the government.
Abdul Razak, known to be well-connected in the local political circle, was last year acquitted of abetting Altantuya's murder.
The prosecution had contended that the murder was ordered by Abdul Razak after their affair ended.
Although he was acquitted, the trial failed to explain what motive the policemen could have had for killing the woman, whose remains were found in a jungle clearing near Shah Alam, the capital of the central state of Selangor.
Abdul Razak, 48, reportedly moved to Britain after the acquittal.
'Just a scapegoat'
Sirul Azhar gave a tearful testimony during the trial, saying he had been made a scapegoat in the case.
He refused to testify under oath, but only read out a statement insisting he was innocent and was "just a scapegoat who has to be sacrificed to cover up the ill intentions of those who were not in court".
Thursday's verdict closes another chapter in a case that has riveted the nation, become fodder for the opposition's election campaigns and spawned intense public speculation about political conspiracies and sex scandals in the corridors of power.
"The international community cannot accept that only these two men were responsible," Karpal Singh, a lawyer for Shaariibuu's family, said.
"It goes beyond that. This is not the end of the road."