President Hugo Chavez said Venezuela's addition as the world's fifth-largest exporter of oil would bring great potential to the bloc founded by Argentina, Brazil, Uruguay and Paraguay in the 1990s.
"This is something that is historic for us ... we are going to work very hard," Chavez said on Saturday while attending a summit of Iberoamerican leaders in Salamanca, Spain. The announcement was also reported by Venezuela's state-run Bolivarian News Agency.
Venezuela - along with Peru, Bolivia and Chile - now holds associate member status, which blocks it from participating in many important Mercosur tariff agreements.
Venezuela's addition will be formalised in December in
Montevideo, Uruguay, during the bloc's annual summit, Chavez said.
Chavez, a fierce critic of US-backed free trade policies in the region, has called for closer regional integration, including seeking support for his own proposal - the Bolivarian Alternative for the Americas trade pact, or ALBA for its Spanish initials, named after Latin American independence hero Simon Bolivar.