The US citizen of Chechen descent was sentenced to death on six counts for perpetrating the Marathon bombings, one of the bloodiest assaults on US soil since the September 11, 2001 attacks.
"I would like to now apologize to the victims and to the survivors," said the 21-year-old former university student in his first public remarks since the April 15, 2013 bombings that killed three people.
"I am guilty," he said in a slight Russian accent, standing pale and thin in a dark blazer. "Let there be no doubt about that."
Judge George O'Toole officially imposed the death sentence, which had been reached unanimously by a 12-person jury on May 15 after prosecutors painted Tsarnaev as a remorseless terrorist.
"I sentence you to the penalty of death by execution," O'Toole told Tsarnaev, before he was led away by US Marshals.
Tsarnaev will eventually sit on federal death row in Terre Haute, Indiana, but prosecutors say he could be sent first to America's only "super-max" prison, ADX Florence, in Colorado.
