After deliberating for 15 hours, the federal jury chose death by lethal injection for Tsarnaev, 21, over its only other option: life in prison without possibility of release.
The same jury found Tsarnaev guilty last month of placing a pair of homemade pressure-cooker bombs on April 15, 2013, as well as fatally shooting a policeman. The bombing was one of the highest-profile attacks on U.S. soil since Sept. 11, 2001.
Tsarnaev, dressed in a dark sport coat and light-colored shirt, stood quietly as the sentence was read, remaining expressionless as he had throughout most of the trial.
U.S. District Judge George O'Toole thanked Tsarnaev for his "composure and propriety."
During 10 weeks of testimony, jurors heard from about 150 witnesses, including people whose legs were torn off by the shrapnel-filled bombs. William Richard, the father of bombing victim Martin Richard, described the decision to leave his 8-year-old son to die of his wounds so that he could save the life of his daughter, Jane, who lost a leg but survived.
Prosecutors described the former high school wrestler, who is an ethnic Chechen, as an adherent of al Qaeda's militant Islamist views who carried out the attack as an act of retribution for U.S. military campaigns in Muslim-dominated countries.
"The defendant claimed to be acting on behalf of all Muslims. This was not a religious crime," said Carmen Ortiz, the top federal prosecutor in Boston. "It was a political crime designed to intimidate and coerce the United States."
Defense attorneys opened the trial on March 5 with the admission that Tsarnaev committed all the crimes he was accused of. But they argued that he was a junior partner in a scheme hatched and run by his 26-year-old brother, Tamerlan. Tamerlan died after the gunfight, which ended when Dzhokhar ran him over with a stolen car.
The jury found Tsarnaev deserved execution for six of the 17 capital charges of which he was found guilty. Those counts were the ones tied to the bomb that he personally placed at the marathon finish line, which killed Richard and 23-year-old Chinese exchange student Lingzi Lu.
The jury did not find him deserving of death for the crimes tied to the bomb placed by his brother, which killed 29-year-old restaurant manager Krystle Campbell, or for the fatal shooting of Massachusetts Institute of Technology police officer Sean Collier, 26.
Tsarnaev's attorneys left the courthouse without commenting to reporters.
The jury's decision does not mean that death is imminent for Tsarnaev. O'Toole will formally sentence him to death at a hearing sometime in the next few months. Defense attorneys are likely to appeal the decision.
The death penalty remains highly controversial in Massachusetts, which has not put anyone to death in almost 70 years and which abolished capital punishment for state crimes in 1984. Tsarnaev was tried under federal law, which allows for lethal injection as a punishment.
Polls had shown that a majority of Boston-area residents opposed executing Tsarnaev. Opponents included Martin Richard's family and Collier's sister.
Just three of the 74 people sentenced to death in the United States for federal crimes since 1988 have been executed. The first was Timothy McVeigh, put to death in June 2001 for killing 168 people in his 1995 attack on the federal government office building in Oklahoma City.
Other people convicted of attacks labeled as terrorist by the U.S. government, including 9/11 conspirator Zacarias Moussaoui and shoe-bomber Richard Reid, drew life prison sentences.
BOSTON'S DARKEST RECENT MEMORIES
The jury was repeatedly shown videos of the blinding flashes and deafening explosions when the bombs went off, followed by screams of fear and pain, pools of blood and frenzied efforts by first responders to save the lives of the 18 people who lost limbs in the attack.
They also heard about the 24 hours of chaos that followed the assassination-style killing of Collier. Hundreds of thousands of residents of greater Boston were ordered to stay in their homes as law enforcement officers hunted for Tsarnaev.
Richard Donohue, a transit police officer who was badly wounded during the manhunt, said, "the verdict, undoubtedly a difficult decision for the jury, gives me relief and closure as well as the ability to keep moving forward."
Tsarnaev himself was impassive throughout the trial, and did not testify in his own defense. He showed emotion only once, when his 64-year-old aunt, Patimat Suleimanova, who had traveled from Russia to testify, broke down in tears on the witness stand upon seeing her nephew. She was unable to compose herself and was excused.
A Roman Catholic nun who is a prominent opponent of the death penalty, Sister Helen Prejean, testified she had met with Tsarnaev and he told her "no one deserves to suffer" as his victims had. Prejean, a Nobel Peace Prize nominee, said she believed he was "genuinely sorry" for his actions.