By Grant McCool and Martha Graybow

NEW YORK (Reuters) - Disgraced financier Bernard Madoff was sentenced to 150 years in prison on Monday for perpetrating the biggest and most brazen investment fraud in Wall Street history.

The courtroom erupted in cheers and applause as U.S. District Court Judge Denny Chin imposed the maximum possible prison sentence on the 71-year-old defendant.

Madoff stood facing the judge with his hands clasped in front of him as he learned his fate.

"The fraud here was staggering," Chin said, after listening to angry statements from some of Madoff's victims.

Before his sentencing, Madoff addressed the court.

"I cannot offer you an excuse for my behavior," he said, speaking in a calm voice. "How do you excuse betraying thousands of investors who entrusted me with their life savings?"

Wearing a dark business suit, leaning forward with his hands resting on a table, he said he tried to undo his crimes but "the harder I tried, the deeper a hole I dug for myself."

He added, "I live in a tormented state now, knowing the pain and suffering I have created."

Earlier, Madoff sat still, his eyes lowered, as victims came before the judge to tell how they were ruined financially, many having to sell their homes and live off Social Security.

"How could somebody do this to us? How could this be real? We did nothing wrong," said Dominic Ambrosino, a retired New York City corrections officer. "We will have to sell our home and hope to survive on Social Security alone."

"You have left your children with a legacy of shame," said Tom FitzMaurice, 63, calling Madoff "an evil low-life."

"He has shown no remorse ... His crime was premeditated and calculated. He was planning to scam investors days before his arrest. If he could, he would still be stealing from investors," FitzMaurice said.

"He cheated investors out of money so that he had his wife Ruth and two sons could live a life of luxury," he said.

Madoff confessed to running a multibillion-dollar "Ponzi scheme" in which investors were paid returns from money paid by later investors.

Investigators do not know how much was stolen, according to court papers. Prosecutors say $170 billion flowed through the principal Madoff account over decades, and that weeks before the financier's December arrest the firm's statements showed a total of $65 billion in accounts.

The trustee winding down the Madoff firm has so far collected $1.2 billion to return to investors.

(Reporting by Grant McCool and Martha Graybow; editing by John Wallace)