A Boston jury found him guilty on all 30 charges and the same jurors will now be asked to decide whether the 21-year-old should be executed by lethal injection.
Tsarnaev, a US citizen who came to America as a child refugee from Kyrgyzstan, stood with his slightly bowed as he listened to the jury`s verdict being read out. The 12 jurors - seven women and five men - took a day and a half to reach their verdict.
Behind Tsarnaev sat family members of the victims, including the parents of Martin Richard, an eight-year-old boy who was the youngest person to die in the attack.
Tsarnaev, who was just 19 at the time of the bombing, planted two homemade explosives at the race finish line alongside his elder brother Tamerlan on April 15, 2013.
The pair fled the scene of the bombing and three days later they murdered a university police officer in a failed attempt to steal his gun. They were finally cornered on a suburban street where they tried to fight off police with a pistol and explosives.
Tamerlan was killed during the confrontation but Tsarnaev escaped and was found the next day hiding in a boat. Although badly wounded and losing blood, the teenager had scrawled messages into the boat`s hull justifying the terror attack.
"Know you are fighting men who look into the barrel of your gun and see heaven," he wrote. "We are promised victory and we will surely get it."
Over the course of a month of testimony, the jury heard from survivors of the bombing, some of whom walked into the court on prosthetic legs after their own were blown off.
The court was shown graphic videos of the moment the bombs exploded and listened to the jihadist chants that the US government says motivated Tsarnaev to carry out the attack.
One of the most moving moments came during the testimony of Bill Richard, the father of Martin. He described how he had to leave his dying son`s side to tend to the wounds of his grievously injured daughter, Jane.
The little girl survived the attack but lost her leg, while Mr Richard`s wife was left blind in one eye.
“I saw a little boy who had his body severely damaged by an explosion and I just knew from what I saw that there was no chance,” Mr Richard told the jurors. “I knew in my head that I needed to act quickly or we might not only lose Martin but we might also lose Jane, too.”
The defence called only four witnesses compared to the 92 called by the prosecution. Their focus instead is on the forthcoming fight to prevent Tsarnaev from being executed.
Both the defence and the prosecution will call new witnesses during the sentencing phase of the trial, which is expected to last at least a month.
The jury must decide unanimously if it decides to sentence him to death and the objections of even one juror could prevent a death sentence from being carried out.
If he is spared the death penalty, Tsarnaev will be sentenced to life imprisonment.
Survivors of the attack, which left 17 people needing amputations and wounded more than 200, said they were pleased with the verdict but there was no clear consensus on whether they wanted Tsarnaev to die.
Jeffrey Bauman, who lost his leg in the bombing and later testified during the trial, said: "Today`s verdict will never replace the lives that were lost and so dramatically changed, but it is a relief, and one step closer to closure."
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