The federal jury unanimously chose death by lethal injection for Tsarnaev, a Kyrgyzstan-born US citizen, over the only other option: life in prison without possibility of release, Xinhua news agency reported.
The same panel of seven women and five men convicted Tsarnaev last month of all 30 charges against him, including 17 counts that carried the death penalty.
Tsarnaev had no expression as a court clerk read the verdict sentencing him to death, local media The Boston Globe reported.
The sentence came down exactly 25 months after the April 15, 2013 bombings, one of the bloodiest attacks in America since the Sept. 11, 2001 attacks.
Tsarnaev was 19 when carried out a twin deadly bombings with his older brother Tamerlan Tsarnaev at the crowded finishing line at the signature event of Boston Marathon.
Three people were killed in the bombings and 264 more were severely injured.