He also said his government will "always work for the safety and welfare of every Indian".
"We welcome today's verdict in the ICJ. Truth and justice have prevailed. Congratulations to the ICJ for a verdict based on extensive study of facts. I am sure Kulbhushan Jadhav will get justice. Our government will always work for the safety and welfare of every Indian," Modi tweeted.
The Prime Minister's remarks came soon after the ICJ put on hold the death sentence of Jadhav.
In a major victory for India, the ICJ ruled that Pakistan must review the death sentence for Jadhav pronounced by a Pakistani military court.
Jadhav, 49, a retired Indian Navy officer, was sentenced to death on charges of "espionage and terrorism" after a closed trial in April 2017. His sentencing evoked a sharp reaction in India.
A bench led by President of the court Judge Abdulqawi Ahmed Yusuf ordered an "effective review and reconsideration of the conviction and sentence of Mr Kulbhushan Sudhir Jadhav".
In November 2008, India and Pakistan inked a bilateral agreement on consular access to their prisoners in each others' countries.