Mozambican President Armando Guebuza presided over a ceremony Sunday in Moatize, in western Tete province.
Vale has invested $1.7 billion in the project. Officials say the mine will begin exporting coal later this year.
Output is expected to start at about one million tons annually and eventually increase to roughly 11 million tons a year.
The southern African country has billions of tons of coal reserves, but until now they have been largely untapped.
Later this year, India’s Tata Steel and Australia’s Riversdale Mining are expected to jointly open another major coal mine in nearby Benga.
Officials say that mine will eventually export million of tons of coal per year, although there are conflicting reports about the exact number.
Mozambique remains one of the world’s poorest countries. Per-capita annual income is about $900, one of the lowest levels in Africa.
The country has been wracked by poverty since gaining independence from Portugal in 1975 after years of civil war.