Movement for Democratic Change (MDC) national chairman Isaac Matongo declared the unopposed nomination of Mr Tsvangirai after a two-day convention in the capital.
Mr Tsvangirai spoke to thousands of supporters pledging to "lead from the front" in protests attempting to topple President Mugabe’s regime.
The MDC leader also lamented the deteriorating standards of living among the majority of Zimbabweans.
“I promise to use all available resources and will power to see off the tyranny in Zimbabwe today," Mr Tsvangirai said.
"We must resolve this national crisis. The dictator must brace himself for a long, bustling winter across the country. The bustle should lead us to a bright political season," he said to applause from the audience.
"A storm is on the horizon," he warned. Mr Tsvangirai did not say in what form and when the protests would take place but urged Zimbabweans to stock up provisions in anticipation of the protests.
Earlier at the convention he said: "I call upon you to heed calls ... for a sustained cold season of peaceful democratic resistance."
The opposition leader said the country's electoral system and judiciary had failed the party, denying it clear victory in the 2000 parliamentary elections and a 2002 presidential poll.
"We need a short, sharp, programme of action to free ourselves," said the former trade union leader who has led the MDC since its formation more than six years ago.