The Pakistan-American is charged on six counts of conspiracy involving Mumbai terror attacks, murdering and maiming persons in India and providing material support to foreign terrorist plots and LeT and six counts of aiding and abetting the murder of US citizens in India.
All the 12 counts of terror changes carries death penalty if convicted.
However, in the wake of his guilty plea, the federal prosecutors have ruled out death penalty.
Headley will not be extradited to India, Pakistan and Denmark if he cooperates with the government's terrorism investigations.
"Headley will cooperate in foreign investigation conducted in the US," his lawyer John Theis told reporters after the hearing.
According to media reports, Headley will testify for the 26/11 trial through video conferencing.
Headley also admitted to using the immigration firm of co-accused Tahawuur Hussain Rana for surveillance activities in India and Denmark.
49-year-old Headley also admitted to be conspiring terror attacks in Mumbai in Nov 2008 and also on a Danish newspaper.
He admitted that he had attended training camps in Pakistan operated by Lashkar-e-Taiba on five separate occasions between 2002 and 2005.
A 35-page plea agreement containing a detailed recitation of Headley's participation in terror conspiracies was presented when the accused changed 'not guilty plea' to 'guilty.
Headley and Tahawwur Hussain Rana were arrested by the FBI on Oct 3, 2009.