Convicted mob boss James "Whitey" Bulger will spend the rest of his life in prison after a US judge sentenced him to serve two life terms plus five years for crimes he committed, including 11 murders.

"The scope, the callousness, the depravity of your crimes are almost unfathomable," US District Judge Denise Casper told Bulger.

The 84-year-old was convicted in August on charges including racketeering, extortion, drug dealing and other crimes as he ran Boston's Winter Hill crime gang in the 1970s and 1980s.

Bulger stood silently as his sentence was read.

Attorneys for Bulger declined to speak on his behalf at the two-day sentencing hearing, saying their client had instructed them not to participate in a proceeding he viewed as "a sham".

After a two-month trial, Bulger was found guilty of 31 of 32 criminal counts, including 11 of the 19 murders prosecutors had accused him of committing.

Bulger's trial was broken by outbursts in which former gang mates-turned-prosecution witnesses swore at the man who was on the run for 16 years.

During today's hearing, he spoke only once, replying "Yes," when Judge Casper asked if he understood he had a right to appeal the verdict.

Bulger's story has captivated the city's residents for years.

He rose from a South Boston housing project to become the most feared person in the city at the same time that his brother, William, became the powerful president of the state senate.

His life inspired Martin Scorsese's 2006 Academy Award-winning film "The Departed".

"The testimony of human suffering that you and your associates inflicted on others was at times agonising to hear and painful to watch," Judge Casper said.

"At times during the trial I wished that we were watching a movie, that what we were hearing was not real," he added.