Hashemi, a senior Sunni Muslim politician, fled Iraq after the authorities issued a warrant for his arrest in December, a move that threatened to collapse a fragile power-sharing deal among Shi'ite, Sunni and Kurdish blocs at a time when U.S. troops were pulling out.
Hashemi, who is unlikely to return to Iraq from Turkey, had accused Shi'ite Prime Minister Nuri al-Maliki of orchestrating a crackdown on Sunni opponents and refused to appear in a court he dismissed as biased.
He and his son-in-law were both found guilty in absentia of murdering a female lawyer and security official, Abdul-Sattar al-Birqdar, a judiciary spokesman said.
"This is a political decision. All our respect to the Iraqi judicial system, but this was political," said lawmaker Jaber al-Jaberi, a member of Hashemi's Sunni-backed Iraqiya party.
Hashemi's lawyer said there would be no appeal because the trial was conducted in absentia.
Since the last U.S. troops left, Maliki's Shi'ite-led government has been politically deadlocked and insurgents continue to strike, hoping to ignite the kind of sectarian tensions that drove Iraq close to civil war in 2006-2007.
Hours before the sentencing was announced, a wave of bombings and shootings killed at least 58 people across the country from the northern city of Kirkuk to southern Nassiriya where a car bomb hit a French consular office.
After the court ruling, four more car bombs hit mainly Shi'ite Baghdad neighbourhoods, killing another 24 people, one blast outside a restaurant and another in a busy commercial district, police said.
The most serious of the earlier bombings happened near the city of Amara, 300 km (185 miles) south of the capital, when two car bombs exploded outside a Shi'ite shrine and a market place, killing at least 16 people, officials said.
With its main hospital overflowing with the injured, mosques in Amara used prayer loudspeakers to call for blood donations.
More were killed in bombings in the towns of Kirkuk, Baquba, Samarra, Basra and Tuz Khurmato, and there was also a strike on an army base and a bombing of security guard recruits for the Iraqi North Oil Company.
The car bomb outside the building housing the French consular office in Nassiriya, 300 km south of Baghdad, killed a police guard and wounded four, authorities said. The consul, an Iraqi citizen, was not at the office.
SECTARIAN TENSIONS
After the fall of Sunni dictator Saddam Hussein and the rise to power of Iraq's Shi'ite majority, many Iraqi Sunnis feel they have been sidelined.
Sunni politicians say Maliki is failing to live up to agreements to share government power among the parties, a charge his backers dismiss by pointing to Sunnis in key posts.
When the Hashemi charges were announced at the end of last year, his Iraqiya party called for a boycott of parliament and the cabinet. But the party has since splintered further.
Heightened political tension is often accompanied by a surge in violence as Sunni Islamist insurgents try to capitalise on instability to strike at the government, local security forces and Shi'ite religious targets.
Violence in Iraq has eased since the dark days of sectarian slaughter after the 2003 invasion to topple Saddam. But insurgents are still carrying out at least one major coordinated attack a month.
Infighting in the religiously mixed government, and a resurgence of a local al Qaeda wing, are raising fears of a return to wider violence, especially as Iraq is struggling to contain spillover from Syria's crisis over the border.
Iraq's local al Qaeda affiliate, Islamic State of Iraq, has claimed responsibility for major attacks on security forces and Shi'ite neighbourhoods. Former members of Saddam's outlawed Baathist party and other Sunni Islamist groups are also fighting the government.
