The incident is expected to further deteriorate already strained Indo-Pak ties which were hit after deadly attacks in Pathankot and Uri by Pakistan-based terrorists last year.
The death sentence to Jadhav, 46, was confirmed by army chief Gen Qamar Javed Bajwa after the Field General Court Martial (FGCM) found him guilty of "all the charges", said the military's media wing Inter-Services Public Relations (ISPR).
Reacting strongly, Foreign Secretary S Jaishankar in New Delhi summoned Pakistan High Commissioner to India Abdul Basit and gave a demarche, which said the proceedings that have led to the sentence against Jadhav are "farcical in the absence of any credible evidence" against him.
He said Jadhav was kidnapped last year from Iran and his subsequent presence in Pakistan has never been "explained credibly".
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The Pakistan Army had also released a "confessional video" of Jadhav after his arrest.
India had acknowledged that Jadhav had served with the navy but denied that he has any connection with the government.
India, through its High Commission in Islamabad, has repeatedly sought consular access to him, as provided for by international law and 13 such requests were formally made between 25 March 2016 and 31 March 2017, the demarche said.
The proceedings that have led to the sentence against Jadhav are "farcical in the absence of any credible evidence" against him, it said, adding it is significant that Indian High Commission was not even informed that Jadhav was being brought to trial.
According to the ISPR statement, Jadhav, a commander in the Indian Navy, "confessed" before a Magistrate and the court that he was "tasked by RAW to plan, coordinate and organise espionage/sabotage activities aiming to destabilise and wage war against Pakistan by impeding the efforts of Law Enforcement Agencies for restoring peace in Balochistan and Karachi."
"Senior Pakistani figures have themselves cast doubt about the adequacy of evidence. The claim in the ISPR release that Jadhav was provided with a defending officer during the so-called trial is clearly absurd in the circumstances.
"If this sentence against an Indian citizen, awarded without observing basic norms of law and justice, is carried out, the Government and people of India will regard it as a case of premeditated murder," the foreign secretary said in the demarche.
India and Pakistan have been at loggerheads over several issues, including on Islamabad's support to terrorism, since the terror attack on an Indian army base in Uri in Kashmir in September last year by Pakistan-based militants killed 18 Indian soldiers.
The two sides were also engaged in a war of words last year over Pakistan's provocative statements on the turmoil in Kashmir following the killing of Hizbul Mujahideen commander Burhan Wani in July last year.