G20 leaders are to meet in the southern French resort of Cannes in early November.
"Ahead of the Cannes summit, we will come out with a proposal for a European financial transaction tax and we are committed to explore this further also at the G20 level," Barroso said in a televised address. He said he would discuss the issue with Australia during his visit there next week.
Money from such a tax could also be used to help finance the European Union's long-term budget, Barroso said, adding the Commission would make appropriate proposals in the next months.
EU officials have indicated that the tax will be first introduced EU-wide and will be used as a stepping stone to convince G20 partners to follow suit. A financial tax, the argument goes, would help hinder speculation on the euro zone's sovereign debt and will have limited economic impact if set at a low enough rate.
"We know it will be difficult, we know there needs to be unanimity [among EU member states]," Commissioner Michel Barnier, in charge of the internal market, told members of the press recently.
France and Germany are already working on a joint proposal for such a transaction tax as part of a bilateral drive for closer economic coordination between euro zone states.
European banks have poured scorn on the idea of a financial transaction tax, a long-standing French proposal, saying it would not stabilise markets.
European Central Bank President Jean-Claude Trichet has said that such a tax would not work unless it is applied globally and Britain, home to the region's biggest financial centre, is also opposed to the EU going it alone.
EurActiv with Reuters
