'Intent on destroying'
The judges said Popovic, who was the chief of security for the Bosnian Serb Army, organised and watched the execution of prisoners.
He "knew that the intent was not just to kill those who had fallen into the hands of Bosnian Serb forces, but to kill as many as possible," the judgment said.
It added that Beara co-ordinated the murder of Muslim prisoners and organised their mass burials, saying he "was intent on destroying a group by killing all the members of it within his reach".
The slaughter in Srebrenica, a UN-protected enclave overrun by Bosnian Serb forces, was the worst massacre on European soil since World War Two.
Tens of thousands of civilians were evicted from their homes, in what the UN court has called a deliberate attempt to wipe out the Muslim community from that area.
Four other military officers and a police official found guilty of related offences were also given jail sentences for between five and 35 years by the UN court on Thursday.
Ljubomir Borovcanin, 50, deputy commander of a special Bosnian Serb police unit, was sentenced to 17 years, Vinko Pandurevic, 50, commander of the brigade that led the Srebrenica attack, got 13 years and Drago Nikolic, 52, the brigade's chief of security, was given 35 years in jail.
Nikolic, Popovic and Beara were all in the chain of command under General Ratko Mladic, the Bosnian Serb commander who remains a fugitive 15 years after his indictment.
Radivoje Miletic, 61, and Milan Gvero, 71, generals in the Bosnian Serb Army high command, were jailed for 19 and five years respectively for crimes against humanity.
All seven had pleaded not guilty.
Survivors of the massacre have welcomed the sentences, saying they were crucial for Bosnia's future
Zumra Sehomerovic from the Mothers of Srebrenica, an association of massacre survivors, said she welcomed the sentences.
"We are satisfied that they have been jailed for life for genocide," she told the AFP news agency.
"The crimes committed in Srebrenica have to be punished for [Bosnia's] future and co-existence," between its ethnic communities, Sehomerovic added.
It was the largest trial conducted at the ICTY to date, with 315 people testifying in court proceedings that began in August 2006.
The verdict could have an indirect bearing on the trial of Radovan Karadzic, the former Bosnian Serb leader, which began last year following his capture in Belgrade in 2008.
Karadzic, 64, is on trial for 11 counts of war crimes, crimes against humanity and genocide charges including the Srebrenica massacre.
In recent months, Serbia has stepped up its efforts to arrest Ratko Mladic, accused by the ICTY of masterminding the 44-month siege of Sarajevo and the