While Kasab is the only survivor of the 10 Pakistani terrorists who created mayhem in the city in November 2008, 30-year-old Sayed Zabiuddin Ansari alias Abu Jundal is accused of participating in the Nov 26-29, 2008, attack's conspiracy allegedly hatched in Pakistan.
He is believed to have issued directions to the terrorists during the attacks, sitting in a "control room" in Karachi.
Special Public Prosecutor Ujjawal Nikam confirmed the development.
Sources in the Crime Branch said that a joint interrogation of Kasab and Jundal will take place at the Arthur Road jail where Kasab is currently lodged.
On July 21, Jundal was taken to Mumbai after a Delhi court handed over his custody to Mumbai Police for his alleged role in the Mumbai terror attack.
The Crime Branch had sought permission for a joint interrogation of Kasab and Jundal earlier this week, which was Thursday granted by the state home department.
Jundal is also an accused in other cases in Maharashtra, including the 2006 Aurangabad arms haul case, the 2010 German Bakery blast in Pune, and an alleged plot to attack Police Academy at Nashik.
Sources said that Jundal also met Lashkar-e-Taiba"s American operative David Headley, a co-accused in the 26/11 attacks. Kasab will be confronted with these revelations to corroborate the version of Jundal.
Jundal is in Crime Branch custody till August 13.