The news came as Myanmar's de facto leader, Aung San Suu Kyi, arrived in Washington on her first official visit.
Myanmar's access to trade benefits for poorer nations had been suspended in 1989 over human rights abuses.
President Obama said the country should now be allowed to benefit from preferential tariffs as it emerges from decades of military rule.
He confirmed the move in a letter to Congress on Wednesday, adding Myanmar - also known as Burma - to the Generalised System of Preferences, a list which exempts certain countries from high import taxes.