The sentences were the first for any of the scores of suspects arrested in the July rioting between Muslim Uighurs and members of the Han Chinese majority in the regional capital of Urumqi. It was China's worst communal violence in decades.
The verdicts appeared aimed at placating Han Chinese who have rallied in Urumqi calling for swift justice. An overseas Uighur activist, however, said they were only likely to exacerbate the ethnic tensions.
Xinjiang has been under heavy security since the strife, and state TV showed paramilitary troops in riot gear surrounding the courthouse Monday.
The official Xinhua News Agency said seven people were convicted of murder, and some also convicted of arson and robbery. Six received the death penalty: Abdukerim Abduwayit, Gheni Yusup, Abdulla Mettohti, Adil Rozi, Nureli Wuxiu'er, and Alim Metyusup.
A seventh man - Tayirejan Abulimit - got a lesser life imprisonment because he had aided in the capture of another man, confirmed Li Jie, a spokesman for the Xinjiang regional government.
The names of the convicted men appeared to identify them as Uighurs.
Xinhua said Abdukerim Abduwayit had used a dagger and pipe wrench to kill five people during the riot, and he also set fire to a building. Gheni Yusup led Abdulla Mettohti, Adil Rozi and Nureli Wuxiu'er in beating four people to death and injuring another. They looted and set ablaze vehicles and shops, killing five people who were inside.
In another attack, Alim Metyusup and Tayirejan Abulimit killed three others and robbed them of their cell phones, Xinhua reported.
Public prosecutors presented witness testimony, autopsy reports, crime scene video and other evidence during the trial attended by some 400 people.
Police have said hundreds of people were detained following the rioting in Urumqi that the government says killed 197 people and injured more than 1,700. State media has reported that 21 people - mostly Uighurs - have been indicted on charges including murder and arson.
The violence flared on July 5 after police broke up a protest by Uighur youths demanding an investigation into a deadly brawl between Han and Uighur workers at a toy factory thousands of miles (kilometers) away in southern China.
Angry Uighurs attacked random bystanders in Urumqi, an overwhelmingly Han city in the heart of the Uighurs' traditional homeland. Two days later, Han vigilantes carried out revenge attacks in Uighur neighborhoods as security forces struggled to restore order.
The Chinese government blames the rioting on overseas-based groups agitating for greater Uighur rights in Xinjiang but has presented no direct evidence.
Many Uighurs have long complained of religious, political and cultural oppression by Chinese authorities, aggravated by large-scale Han migration into the region since the imposition of communist rule in 1949.
Dilxat Raxit, spokesman for the Germany-based World Uighur Congress, called the verdicts flawed and said they would likely aggravate tensions in the region. The timing appeared to indicate that China wanted the matter closed prior to next month's visit by President Barack Obama, he said.
"These verdicts were motivated by politics, not the desire to see justice served," said Raxit, who added the men could not have had a proper legal defense because their lawyers were appointed by the court.
Swift punishment of those arrested over the rioting were among the demands of Han protesters who swarmed into Urumqi's streets early last month calling for the firing of Xinjiang's powerful Communist Party boss Wang Lequan.
Wang, an ally of Chinese President Hu Jintao, held on to his job but Urumqi's party boss and Xinjiang's chief of police were both replaced.
Protesters had also demanded an end to a string of bizarre needle stabbings that had spread fear and panic throughout the region. Police quickly arrested a number of suspects in the attacks and an Urumqi court has sentenced seven to prison terms of up to 15 years.
Monday's sentences came three days after a Chinese court in southern China sentenced a man to death for his role in the factory brawl that sparked the riots in Xinjiang.