A Frankfurt court has jailed an Islamic State militant for life for genocide against the Yazidi minority, the first legal case worldwide to deliver a genocide verdict in relation to the Yazidi community.

29-year-old Taha Al-Jumailly was found guilty of genocide, crimes against humanity resulting in death and war crimes after he had chained a five-year-old girl to an outside window in 50-degree temperatures.

This was one case in a non-descript courtroom in Frankfurt, but it is an enormous step forward for the beleaguered Yazidi community.

Taha Al-Jumailly, a native of Iraq who had joined Islamic State in Mosul, was accused of having purchased a Yazidi woman and her daughter as slaves.

Later, when they moved to Fallujah he had chained the five-year-old girl to a window outdoors in soaring heat.

The girl died of thirst and in agony, the court heard.

In October, Al-Jumailly's one-time German wife Jennifer Wenisch, who had joined him in Iraq, was jailed for ten years by a Munich court for crimes against humanity for her part in the enslavement.

The Yazidis, an ancient minority with their own religion, are centred around disputed Kurdish regions of Iraq, Iran, Syria and Turkey. They have been mercilessly persecuted by Islamists, and during the Syrian civil war Islamic State killed hundreds of men, raped women and forcibly recruited children as fighters.

International human rights lawyer Amal Clooney represented the girl's mother in the case. She said the verdict was a victory for everyone who believed in justice.

After the verdict, the public prosecutor said the verdict sent out a strong signal worldwide that Islamic State’s actions against the members of the Yazidi religion constituted genocide.

German courts have used the legal principle of universal jurisdiction, allowing prosecutions of crimes perpetrated elsewhere.

Germany, which is home to a large Yazidi community, is one of the few countries to have taken legal action over such abuses.

The courts there have already handed down five convictions against women for crimes against humanity related to the Yazidis committed in territories held by IS.

Prosecutors in Naumburg on Tuesday charged a German woman named as Leonora M with aiding and abetting crimes against humanity after she and her IS husband enslaved a Yazidi woman in Syria in 2015.

Today's verdict is a small victory for a community that has undergone centuries of suffering.