It also aims to prevent a spike in global oil prices after an EU embargo on Russian crude takes effect on December 5.
Details of the price cap deal are due to be published in the EU legal journal on Sunday.
In a statement, the group said the price cap would take effect on Monday, or soon after.
The deal was reached after resistance from Poland, which later formed an agreement with other EU members
Warsaw was hoping for a much lower cap, to squeeze revenues to Russia.
The G7 price cap will allow non-EU countries to continue importing seaborne Russian crude.
But it will ban shipping, insurance, and re-insurance companies from handling the cargo, making it difficult for Moscow to sell its oil for a higher price.
U.S. Treasury Secretary Janet Yellen said the cap will immediately "cut into Putin's most important source of revenue."
She added the cap will help low and medium income countries, who have been hit hardest by high energy and food prices.
On Twitter, European Commission President Ursula von der Leyen said the price cap would help stabilize global energy prices.
Russia's lower house foreign affairs committee told Tass news agency that Europe was jeopardizing its energy security.
