The jury deliberated for four hours before finding El Shafee Elsheikh guilty on all counts. Elsheikh stood motionless and gave no visible reaction as the verdict was read.
With boots and gloves, they pick up soggy trash, water bottles, aluminium cans and muddy styrofoam boxes, part of a green activist campaign called the Cleanup Ambassadors.
Iraq's foreign minister earlier had said the fifth round of talks between Saudi and Iranian representatives was due to resume on Wednesday.
"Thanks to the bravery of our troops this horrible terrorist leader is no more," Joe Biden said.
It was one of the boldest attacks by the militants in recent weeks and came amid an uptick in violence that stoked fears the group has been re-energised.
Kuwait Airways suspended flights to Iraq for a week starting Sunday, citing security fears after some six rockets struck the Baghdad airport last week damaging two commercial planes.
The rockets fired in the early morning landed on planes parked in a waiting area of Iraqi Airways, the country's national carrier, the statement said.
The brazen attack more than 120 kilometers (75 miles) north of the capital Baghdad was one of the deadliest targeting the Iraqi military in recent months.
It was a dramatic escalation in the already tense situation following the Oct. 10 vote and the surprising results in which Iran-backed militias lost about two-thirds of their seats.
Alexanda Anon Kotey admitted guilt in connection with the deaths of four American hostages as well as European and Japanese nationals who also were held captive.
Among the invitees are archenemies Iran and Saudi Arabia, whose rivalry has often played out in Iraq and other countries, including Yemen and Lebanon.
A car bomb has struck Baghdad's southwestern al-Bayaa neighbourhood shortly before sunset Thursday, killing 51 and wounding more than 60 others.