Marcel Malanga, Tyler Thompson and Benjamin Zalman-Polun are being held in a military prison in the capital, Kinshasa.
The three Americans, who are aged between 23 and 37, were among 37 people sentenced to death over the alleged May coup attempt, in which armed men attacked a minister's home before heading to presidential offices.
The decision to commute their sentence was read out on state television overnight.
Richard Bondo, Zalman-Polun's lawyer, told AFP they were happy with the presidential decision.
The three Americans now have "the right to hope for a definitive release following a total remission of sentence which is also one of the methods of applying the presidential pardon outlined by the constitution" of the Democratic Republic of Congo, he said.
The alleged coup bid began in the early hours of May 19 last year when several dozen armed men attacked the home of then-economy minister Vital Kamerhe, who is now the national assembly president.
Armed men then went to a building housing Tshisekedi's offices waving flags of Zaire, the country's name under ex-dictator Mobutu Sese Seko, who was overthrown in 1997.
Shots were heard near the building, several sources said at the time.
An army spokesman said later on national television that defence and security forces had stopped "an attempted coup d'etat".
The alleged plot was led by Christian Malanga, a Congolese man who was a "naturalised American" and who was killed by security forces, army spokesman General Sylvain Ekenge has said.
He was the father of Marcel Malanga.
In March last year, the DRC government lifted a moratorium on the death penalty that had been in force since 2003.
It said the move was to target soldiers accused of treason, with the country facing armed rebellion in its troubled east.
Human rights groups criticised the decision.
Since then, more than about 100 death sentences have been handed down but none has so far been carried out.
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