Iraqi sources said Umar Yusuf Jumaa, also known as Abu Anas al-Shami, was killed on Friday in a US air strike targeting his vehicle in Abu Ghraib, Iraq.
Al-Shami, 35, is identified as one of two main persons on the group's website, Aljazeera's correspondent in Amman, Yasir Abu Hilala, said. The other person mentioned on the site is Abu Musab al-Zarqawi who is alleged to have ties to the al-Qaida network.
Described as a prominent Muslim scholar in Jordan, al-Shami is considered the legislative organiser of the group.
Al-Shami, who left Iraq for Jordan after the US-led invasion, is said to have been responsible for issuing fatwas (Islamic edicts) on the website.
The leader, who completed his studies in Kuwait, was arrested twice during his residency in Jordan. Details surrounding those arrests were not available.
The group al-Tawhid and al-Jihad last week captured two Americans and a British man working in Iraq and threatened to behead them unless their demands for female prisoners to be released are met.
The two Americans have since been beheaded and their bodies found by Iraqi police.
Relatives of the British captive are appealing to British and Iraqi officials to heed the captors' demands.