Leaders also announced they would help vulnerable countries to increase food production and called on nations with large stockpiles of food to make some available.
The western leaders said Russia's war in Ukraine was “dramatically aggravating” the food crisis, which is in danger of throwing more than 320 million people into hunger, according to the World Food Programme.
Ukraine and Russia are two of the world's largest agricultural exporters and the war has brought grain shipments via the Black Sea to a standstill, a situation the two sides blame on each other.
Ukraine's western neighbours have salvaged some of the stranded grain by road and rail, but these routes cannot handle the same volume of food and face problems including Ukraine's Soviet-era infrastructure.
Exports of grain are expected to reach about two million tonnes this month, up from 1.2m in April - but this is still still less than the pre-war volume handled by the port of Odesa alone, said French President Emmanuel Macron.
“We will step up our efforts to establish alternative routes,” building on the EU's so-called solidarity lanes via countries such as Romania and Poland, the G7 statement said.
“We commit to sustainably increase the availability of agricultural products including through strengthening agricultural productivity in the most affected countries.”
It comes after the European Union suggested a plan to increase fertiliser production in Africa, similar to the way that vaccine manufacturing was encouraged there during the coronavirus pandemic.
The additional $4.5bn, bringing the total committed this year by G7 countries to $14bn, is earmarked for “protecting the most vulnerable from hunger and malnutrition”.
Tuesday's announcement came a day after G7 leaders were joined by the head of the UN, the African Union and partner countries for talks on the food problem.
Western countries are looking to counter the narrative being pushed by the Kremlin that sanctions on Russia are to blame for the problem.
The G7 said it had put no sanctions on food and the leaders said they would work to stop any spillover effects.