The three are the first IS members from France to face execution.
One reportedly fought for IS in Syria while another was part of a European foreign terrorist fighter cell responsible for attacks in Iraq and Syria and for planning others in Europe, US officials have said.
French investigators said the third member, from Paris, moved his wife and two children to the Iraqi city of Mosul before heading to Syria.
They were among thousands of foreign fighters who joined IS after it declared a caliphate in 2014.
Since Iraq defeated the terrorist group in 2017 many have found themselves being processed through the country’s court system, where membership of the terrorist group is enough to be sentenced to death, regardless of whether a person fought.
In May last year Belgian jihadist Tarik Jadaoun was sentenced to death in Iraq
The three men and 10 other French citizens were handed to Iraqi authorities by the US-backed Syrian Democratic Forces at the beginning of this year.
A court-appointed lawyer said the three had asked to be tried in France but “judges ignored their request”.
Iraq has thousands of its own citizens moving through the courts on terrorism-related charges – most are accused of joining IS in Iraq and hundreds more have been repatriated from Syria.
Iraq has detained or imprisoned at least 19,000 people accused of connections to IS or other terror-related offences, according to analysis by The Associated Press last year.
In April last year a group of Russian women were jailed for life in Baghdad after it was found they were members of IS
More than 3,000 of them have been sentenced to death.
Human rights groups have raised concerns that some of the trials are based on evidence obtained by torture and that courts are not impartial or thorough, with trials sometimes lasting just a few minutes.
The three men’s trials could be a test for how the international community handles the thousands of foreign fighters who were still with Islamic State in its dying days.
France has so far refused to take back IS fighters and their wives, who are described by the country’s foreign minister Jean-Yves Le Drian as “enemies” of the nation.
A small number of children have been repatriated, however.
The French Foreign Ministry declined to comment on Sunday’s death sentences for the three men, who have 30 days to appeal their sentences.
