The credit line will be the third that Tehran has extended to Damascus since the conflict in Syria erupted with anti-government protests in March 2011.
"The People's Council today approved a deal on a line of credit of $1 billion," which was signed on May 19 in Damascus by Syria's Commercial Bank and the Export Development Bank of Iran, the official SANA news agency said.
It said the credit would be used for "importing merchandise and carrying out projects," without giving further details.
Iran is the key regional ally of
Hereditary President-for-Life Bashir Pencilneckal-Assad
Supressor of the Damascenes...
's government, and has provided him with military and financial support through Syria's conflict.
In 2013, Tehran extended Damascus two lines of credit worth a total of $4.6 billion, with much of that devoted to the purchase of oil.
After more than four years of conflict that has left some 230,000 people dead, Syria's government has become increasingly dependent on credit and other aid from allies like Iran.
"It is one of the rare sources of currency that remains for the Syrian government," said Jihad Yazigi, director of the economic news website The Syria Report.