Pakistani citizen Mohammad Ajmal Kasab, 21, had been charged with 86 separate offences including murder and waging war against India in the Nov. 26-28 assault, which killed 166 people and caused tensions to flare between India and Pakistan. The siege ended when troops stormed the Taj Mahal Hotel where some of the gunmen were holed up.
On Monday, Kasab stood up during his trial and told the judge, "Sir, I plead guilty to my crime," triggering a collective gasp in the courtroom, the Associated Press reported.
Judge M.L. Tahiliyani, who also was apparently taken aback, called lawyers from both sides to figure out the significance of Kasab's statement.
In his lengthy statement, Kasab gave details of his group's journey from Pakistan on a boat, their subsequent landing in Mumbai, and the bloody rampage that followed as the gunmen shot and killed people at a railway station, a Jewish center and two five-star hotels, including the Taj Mahal.
He also described how he became a Lashkar-e-Taiba soldier, saying he was working for a pittance at a decorating shop in the town of Jhelum, in Pakistan, a job he hated. He and a friend decided to become armed robbers, reported the New York Times.
Kasab said they went to the garrison city of Rawalpindi, next to Islamabad, where they decided to ask a jihadist group to train them to be militants. They would then use those skills to become expert robbers. They asked around in the city's market for the mujahedeen fighters, and someone directed them to Lashkar-e-Taiba's office.
"I don't think I am innocent," he said toward the end of his confession. "My request is that we end the trial and I be sentenced."
It was not immediately clear what prompted Kasab to make the statement after consistently denying he was guilty.
"Everybody in the court was shocked the moment he said he accepts his crime. It was unexpected," public prosecutor Ujjwal Nikam said, according to the AP.
If the confession holds up in court it will boost India's claims that terrorist groups in Pakistan were behind the attack, and that Islamabad was not doing enough to clamp down on them.
The only one of the 10 gunmen captured alive during the attacks, Kasab is among 38 charged in the attack. India says most of the accused are in Pakistan.
The allegations have severely strained relations between the two nuclear-armed archrivals.
Pakistan has acknowledged the Mumbai attacks were partly plotted on its soil.