"The country is now in your hands," Masum told Abadi, who moments earlier was selected as nominee for prime minister instead of incumbent Nuri al-Maliki by the Shiite National Alliance parliamentary bloc.
Abadi, a member of Maliki's Dawa party who is viewed as close to the two-term premier, was communications minister in the interim government following the overthrow of Saddam Hussein, after spending much of the dictator's rule in exile.
He was elected to parliament in 2006, chaired the finance committee and became deputy parliament speaker earlier this year.
The nomination of Abadi may raise fears of more infighting in the government as the country faces the threat of ISIL terrorists in the north.
Al-Maliki's Shiite-dominated bloc won the most parliament seats in April elections and the prime minister sees himself as rightfully keeping the post.
The president's choice is a very public snubbing of incumbent Prime Minister Nouri el-Maliki who in an angry midnight speech all but demanded he be re-nominated for a third term.
NJF/NJF