The United States, Qatar, Turkey and the European Union led the push for the emergency debate, the UN rights body's fourth special session on Syria since unrest broke out in the country early last year.
Scheduling the debate, which has not yet been officially announced, requires signatures of 16 countries that are members of the Human Rights Council.
"It's all materialising very quickly," said one official. "It's going to have huge support."
Some members plan to draft a text that is likely to condemn Friday's Houla massacre, in which at least 108 people were killed, and demand further investigation.
The massacre, a clear breach of a ceasefire deal brokered by international envoy Kofi Annan, has already prompted at least seven Western nations to expel Syria's envoys from their capitals.
The European Union is likely to press the Human Rights Council to recommend the UN Security Council refer the case to the International Criminal Court (ICC).
"It should be a strong, robust resolution because what has happened is just intolerable," one EU diplomat said.
China and Russia, which have the power to veto any U.N. sanctions against Syria, have refused to blame forces loyal to Syrian President Bashar al-Assad for the Houla killings, so the widespread outrage is unlikely to translate into tough action on the Syrian government.
In the Human Rights Council's last debate on Syria, 41 of the 47 members backed a resolution criticising Syria. Only Russia, China and Cuba voted against.
One month earlier, Syria's ambassador stormed out of the Council during an emergency debate on Syria, blaming foreign countries for inciting sectarianism and providing arms to the opposition in Syria.