'Links to Pakistan'
The three were found guilty in July over the attacks at the Gateway of India monument and in the gold and jewellery quarter of the Zaveri Bazaar.
The bombs were planted in two taxis and exploded within minutes of each other at lunchtime on August 25, 2003.
Police accused the group of being members of the so-called Gujarat Muslim Revenge Force, and said the bombings were retaliation for Hindu attacks on Muslims during riots in Gujarat state in 2002.
Prosecutors said that they also had links to the banned Pakistan-based Lashkar-e-Taiba (LeT) group, which has been accused of planning last November's attack on Mumbai in which at least 166 people died.
The three defendants had pleaded not guilty to all charges.
Two other men accused of providing and assembling the high-explosive RDX devices used in the attacks were previously acquitted by the court.