The US Friday said its justice department decided against seeking death for David Headley because he cooperated with law enforcement authorities over the 26/11 Mumbai attack.
Pakistani American Headley, who played a key role in the 2008 attack, received a 35-year jail term Thursday.
Referring to the sentence without parole of Headley, a US embassy statement said: "It reflects both severe punishment for Headley's role in the heinous 26/11 crimes and a decision by the US Department of Justice not to seek the death penalty.
"This decision was taken because of Headley's willingness to cooperate with law enforcement authorities -- American, Indian and others -- to help bring the perpetrators to justice and prevent other terrorist attacks."
It said Headley provided information that was of substantial value "in our efforts to combat international terrorism and to save lives".
Citing instances, it said Headley testified against a co-conspirator, Tahawwur Rana, who is serving a 14-year sentence.
"Headley provided extensive detail about accused terrorist leader Ilyas Kashmiri and his network. Ilyas Kashmiri was indicted in 2009.
"Headley answered questions from Indian law enforcement.
"Headley assisted US investigators in bringing criminal charges against five other terrorists," the statement said.
It said Headley provided US law enforcement authorities with extensive detail about the structure, personnel, methods, abilities and plans of terrorist group Lashkar-e-Taeba.
Stressing that the counter-terrorism cooperation between India and the US was "stronger than ever", it said the FBI had provided its expertise and testified in the Indian prosecution of Mumbai accused Ajmal Kasab.
It added that Headley's sentence marked another step in its efforts to bring to justice those responsible for the Mumbai attack.
"We are working together to see that those responsible for 26/11 and other acts of terrorism are brought to justice, wherever they may be," it said.