The first round of negotiations for a trans-Atlantic trade agreement between the United States and the European Union will take place next month in Washington, Obama said.
"I believe that we can form an economic alliance as strong as our diplomatic and security alliances," he told reporters after the leaders of eight of the world's most powerful nations kicked off their meeting.
"The whole point of this meeting ... is to fire up our economies and drive growth and prosperity around the world. ... There's no better way than by launching these negotiations on a landmark deal between the European Union and the United states of America," Cameron said.
Cameron, the host of this week's conference, named the problem of tax avoidance by large corporations as a central issue for G8 leaders to resolve at this year's summit. The British prime minister hopes to secure agreements among nations on sharing tax information, with the goal of ensuring global companies aren't able to dodge tax bills.
The measure met resistance from firms' chief executives, though Cameron said he's willing to withstand corporate ire for a fairer global tax system.
"You don't get anywhere unless you are prepared to give the lead and perhaps make a few enemies along the way," Cameron said. "In setting the G8 agenda around trade, tax and transparency, yes, you are taking on some vested interests, you are taking on some difficult decisions. But actually will it help both the developing world and us in the West? I believe it can."
While in Europe, Obama will also likely be forced to defend U.S. Internet surveillance techniques that were disclosed in a series of newspaper articles in early June. The intelligence programs, which were previously considered top secret, involved large tech companies who operate globally, including Facebook, Google and Yahoo.