It took the jury more than 14 hours to choose death on six of the 17 capital counts over life imprisonment for the 21-year-old Muslim former university student of Chechen descent who came to the United States as a child.
The same 12-member panel convicted him on April 8 on all 30 counts relating to the April 15, 2013 bombings, the murder of a police officer, a car jacking and a shootout while on the run.
Tsarnaev went on the run and was arrested four days later, hiding and injured in a grounded boat on which he had scrawled a bloody message apparently defending the attacks as a means to avenge the US wars in Iraq and Afghanistan.
Two years later, he stood in a dark blazer with his hands clasped before him, showing no emotion as the court clerk read from the death penalty.
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The court was silent during the verdict reading.
Prominent survivors had opposed the death penalty for Tsarnaev, a teenager at the time, fearing that lengthy appeals would dredge up their agony.
The federal sentence comes despite widespread opposition to the death penalty in the state of Massachusetts, where no one has been executed since 1947.
Survivors, including the parents of the youngest victim eight-year-old Martin Richard, crammed into the gallery to hear the verdict.
Since the federal death penalty was reinstated in 1988, only 79 people have been sentenced to die and only three have been executed, says the Death Penalty Information Center.
The decision caps a harrowing, more than two-month trial that saw the court relive the horror of the attacks day after day through grisly videos and heartbreaking testimony from those who lost limbs and loved ones.