Tsarnaev faces either life in prison or the death penalty, after a jury unanimously convicted him Wednesday of carrying out the worst attack in the United States since the 9/11 hijackings.
Jurors took a day and a half to find the 21-year-old former student guilty on all 30 counts related to the April 15, 2013 attacks, the murder of a police officer, a car jacking and a shootout while on the run.
The immigrant of Chechen descent, who took US citizenship in 2012, stood in a dark blazer, occasionally fidgeting and hooking one hand into his trouser pocket as the clerk read out the verdict.
He now faces life in prison without parole or even the death penalty when he is sentenced by the same jury at the second phase of the trial, which could start early next week, Judge George O'Toole told the court.
Survivors, including the parents of eight-year-old Martin Richard who was killed in the attacks, crammed into the gallery to hear the verdict as a strict security cordon was set up outside in the biting wind and sleet.
Three people were killed and 264 others wounded, including 17 who lost limbs, in the twin blasts at the city's marathon nearly two years ago.
Tsarnaev went on the run and was arrested four days later, hiding and injured in a boat on which he had scrawled a bloody message apparently justifying the attacks to avenge the US wars in Iraq and Afghanistan.
Survivors welcomed the verdict and thanked the jury after a harrowing month-long trial of grisly videos of the horror after the attacks, and heartbreaking testimony from those who lost limbs and loved ones.