Russia was expelled from what was then called the G8 in 2014 because of its annexation of Crimea from Ukraine. Trump said it should be readmitted.
"You know, whether you like it or not, and it may not be politically correct, but we have a world to run and the G7, which used to be the G8, they threw Russia out, they can let Russia come back in, because we should have Russia at the negotiating table," he told reporters before leaving Washington.
Other G7 leaders, including host Canadian Prime Minister Justin Trudeau, have been critical of Trump’s trade policy ahead of the summit, condemning his administration’s imposition of tariffs on steel and aluminium imported from allies including Canada and the European Union.
Trump’s presidency has been clouded by a federal investigation into Russian meddling into the 2016 presidential election, and possible collusion by Trump’s campaign.
Both Moscow and Trump have denied any such activity.
Trump was scheduled to leave the G7 meeting early on Saturday, to prepare for a summit with North Korean leader Kim Jong Un on Tuesday. The group consists of the United States, Canada, France, Germany, Italy, Japan and Britain.