The retired navy men were arrested last year on suspicion of spying for Israel on Qatar’s military submarine programme, The Times of Israel reported.
The Indian government on Thursday vowed to explore all legal options in the case. The foreign ministry in a statement said it would "take up the verdict with Qatari authorities" and continue to "extend all consular and legal assistance" to the prisoners.
"We are deeply shocked by the verdict of death penalty and are awaiting the detailed judgment," it added.
The eight men were employees of the Al Dahra consulting company, which advises the Qatari government on the acquisition of submarines.
The prisoners have been identified as captain Navtej Singh Gill, captain Birendra Kumar Verma, captain Saurabh Vasisht, commander Amit Nagpal, commander Purnendu Tiwari, commander Sugunakar Pakala, commander Sanjeev Gupta, and Sailor Ragesh, according to The Hindu.
The retired navy officers reportedly had distinguished service records of up to 20 years and held crucial roles, including that of instructors in the force.
Neither the Indian government nor the Qatari authorities have made the charges against the men public. The Qatari authorities previously provided New Delhi consular access to the eight Indian nationals during their trial.
Indian foreign minister Subrahmanyam Jaishankar had earlier said that the exact nature of the charges against the eight men was "not entirely clear".
Thursday's government statement said that it would "not be appropriate to make any further comments at this stage" due to the "confidential nature of the proceedings".
The sentence comes at a time when Israel's offensive in the Gaza Strip in retaliation against Hamas's surprise 7 October attack has killed over 7,000 Palestinians. More than 1,400 people in Israel, mostly civilians, were killed during the initial Hamas attack, according to the Israeli government.
Qatar has been playing a key intermediary role in negotiating the release of several Israeli hostages held in Gaza by the Palestinian militants along with ensuring entrance of humanitarian aid for the Gazans.
More than 800,000 Indian citizens live and work in Qatar.