"I am sure Kulbhushan Jadhav will get justice," PM Modi said.
"Our government will always work for the safety and welfare of every Indian," the prime minister added.
The ICJ had upheld India's stand stating that Pakistan had violated the 1963 Vienna Convention on consular relations while granting India consular access to Jadhav.
Harish Salve, who was representing India in the case had questioned the functioning of Pakistan's military court in the case and had urged the UN court to annul Jadhav's death sentence, which is based on an "extracted confession".
In its sentence, the ICJ asked Pakistan to effectively "review and reconsider the conviction and sentence of Kulbhushan Sudhir Jadhav".
India's former external affairs minister Sushma Swaraj in a series of tweets had hailed the verdict asserting that it was a "great victory for India".
Swaraj said, "I wholeheartedly welcome the verdict of International Court of Justice in the case of Kulbhushan Jadhav. It is a great victory for India."
"I thank the Prime Minister Shri @narendramodi for our initiative to take Jadhav's case before the International Court of Justice. I thank Mr.Harish Salve for presenting India's case before ICJ very effectively and successfully," Swaraj said.
"I hope the verdict will provide the much needed solace to the family members of Kulbhushan Jadhav," Swaraj added.
In its sentence, the ICJ asked Pakistan to effectively 'review and reconsider the conviction and sentence of Kulbhushan Sudhir Jadhav'.