Nearly 300 died in events surrounding the July 15 coup attempt, which triggered a massive government crackdown.
Thousands of alleged supporters of a US based Turkish cleric Fethullah Gulen -- who denied any role in fomenting the coup -- were detained or dismissed from government jobs.
"It is the Turkish parliament that will decide the death penalty... I declare it in advance, I will approve the decision made by the parliament," Recep Tayyip Erdogan told the rally, reports BBC.
Western nations have been critical of the government's response to the coup. The European Union, which Turkey has applied to join, refuses to accept capital punishment in member states.
Speaking at the Democracy and Martyrs' Rally in Istanbul's Yenikapi district, Erdogan said: "Our presence today upsets our enemies just like it did on the morning of July 16.
"On that night there were people who risked their lives to stop the coup and they filled the streets. History will remember names of our martyrs... in golden letters," Anadolu quoted Erdogan as saying.
The "Democracy and Martyrs' Rally" is the climax of three weeks of nightly demonstrations by Erdogan's supporters around the country.
Speaking ahead of Erdogan, Prime Minister Binali Yildirim told the rally that Fethullah Gulen would be brought to Turkey and made to pay the price for the coup attempt.
"Let all of you know, the leader of this terrorist group will come to Turkey and pay for what he did," Yildirim said.
Yildirim said that July 16 coup attempt was Turkey's second War of Independence, adding, "Every coup which does not kill us, makes us stronger. Just like here and now."
The leader of the main secularist opposition party, Kemal Kilicdaroglu, told the rally that the coup had opened a "new door of compromise" in the country's politics, "there is a new Turkey after July 15", the Republican People's Party leader said.
In a rare address to a public rally, the head of Turkey's armed forces, Hulusi Akar, said "traitors" behind the attempted coup would be punished in the harshest way, and thanked civilians for their role in defeating the uprising.
The crackdown in Turkey has seen tens of thousands of public sector workers suspended or dismissed, with many having their passports cancelled. There has also been a massive reshuffle of the military.
Gulen had been a close ally of Erdogan until a bitter split between his movement and the party of the President three years ago.
Turkey has listed Gulen's movement as a terrorist organisation.
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