Lawyer Patrick Baudouin said Zacarius Moussaoui's mother, Aisha el-Wafi, has asked French officials "to intervene with the American authorities to ask that Zacarias Moussaoui serve out his term in a French prison".
Ms Wafi told French radio after the sentence was announced against her son late on Wednesday: "It's the worst thing that could happen to a mother".
She said her son "was convicted for what he said, not what he did".
Earlier, a US jury ruled that Al-Qaeda conspirator Moussaoui should be jailed for life without parole, rejecting the death penalty for his role in the attack conspiracy carried out on September 11, 2001.
Moussaoui shouted "America, you lost, I won," and clapped his hands after the jury in the Virginia court rejected a death sentence against him.
Judge Leonie Brinkema will formally pronounce the sentence against the 37-year-old Frenchman of Moroccan descent later in the day.
Moussaoui is the only person to have been charged in the United States over the 2001 attacks on New York and Washington in which almost 3,000 people died.
The nine men and three women on the jury reached a verdict after a marathon 40 hours of deliberations.
"The jury has found the defendant should be sentenced to life in prison without the possibility of release," said court spokesman Edward Adams speaking on the steps of the court in Alexandria, Virginia, in the suburbs of Washington.
Mr Adams said that the jury verdict form did not indicate how many jurors voted for life in prison and how many in favour of death, if any.
Unanimous verdict needed
The jury had to unanimously agree a verdict to recommend that Moussaoui be sentenced to death.
Prosecutors had argued that Moussaoui's "lethal lies" while in jail prior to the attacks gave his fellow Al-Qaeda conspirators the chance to pull off the spectacular strikes on Washington and New York.
But his lawyers rejected that claim as overblown, and transcripts of closed hearings released late on Tuesday show that their doubts about Moussaoui's truthfulness were partially shared by Judge Brinkema.
"I still think that Moussaoui was not accurate in a lot of what he said about how much he knew about what was going to happen with which particular buildings and when," Judge Brinkema said in the hearing on April 21.
During his trial Moussaoui claimed in blockbuster testimony that he knew the World Trade Center in New York was a key target on September 11.
He also claimed he would have flown a hijacked passenger jet into the White House on that fateful day, had he not been arrested weeks earlier.
But his claim conflicted with all previous knowledge of the strikes on New York and Washington, as well as with Moussaoui's own earlier admission that he was to have been part of a second wave of attacks.
The defence contended that he is a caricature of a terrorist, was rejected by the "real" Al-Qaeda plotters and exaggerated his role in the group.
Defence attorneys also pleaded with jurors not to make a martyr of
Moussaoui and said he should instead be saddled with the "long, slow death of a common criminal" in a maximum-security prison.
Jurors took 18 hours in the first phase of the Moussaoui sentencing trial to decide he was eligible for the death penalty for committing an act, lying, that directly caused the death of at least one person in the attacks.
Jurors had to wrestle in their death penalty phase deliberations with an intricate 42-page verdict form and weigh long lists and aggravating and mitigating factors to reach their decision.
Bush, Guiliani react
Meanwhile US President George W. Bush, asked to comment on the trial, pledged that the United States would "stay on the offensive" against terrorism.
Former New York mayor Rudy Giuliani said he disagreed with a jury's decision to spare Moussaoui’s life.
Mr Giuliani, who was Mayor of New York at the time of the September 11 attacks testified last month in the sentencing trial to recount his horrific memories.
"It seemed like it was a fair trial -- not just the result that I would have come to. He lied to the FBI. If he'd told the truth he could have prevented it. For me, that would make him a material and very important part of the conspiracy," said Mr Giuliani, who became a national hero for his handling of the disaster.
But the former mayor added: "If you believe in this system, you have to be willing to agree with conclusions that you would not share.
"The greater value I think would have been if he was executed. But the greater value is demonstrating what America is like.
"America won tonight," he said, arguing that the United States had upheld the worth of its legal system in the eyes of the world.
Families react
Several relatives September 11 victims said justice was done when jurors sentenced Moussaoui to life in prison rather than being put to death.
Abraham Scott, whose wife, Janice, died in the Pentagon, said he would have told her, "Baby, at least one perpetrator has been brought to justice."
Mr Scott and others said they wanted other members of al-Qaeda brought to justice now that the Moussaoui trial is over.
Rosemary Dillard, whose husband, Eddie, also died in the Pentagon, said the American system of justice worked.
"It's not going to be what all the families want. It shows the world we're not going to stand for terrorists to come to our country and to be let loose," she said.
Carie LeMack, whose mother, Judy Larocque, perished on American Airlines Flight 11, which crashed into the World Trade Centre, said her mum did not believe in the death penalty and would have been glad that he was sentenced to life.