Speaking to a small group of journalists at the World Economic Forum in Davos, Tsvangirai said he expects a referendum on a new constitution around October of this year, leading to elections in 2011.
"I believe that the inclusive government process is a process which is irreversible," he said.
He stressed that foreign investors should be reassured that the country was not sliding backward. "Certainly the country is moving forward, and this is a time to look at the country in a more positive light."
His optimistic comments were in contrast to news last week that Zimbabwe had suspended moves to draw up a new constitution due to political bickering over funding. That was seen as dealing a blow to hopes for free and fair elections next year after the intended adoption of the charter.
Tsvangirai and his arch rival President Robert Mugabe signed a power-sharing agreement in September 2008, which led to formation of the unity government last February and an agreement to write a new constitution within 18 months.
Western donors, expected to provide the bulk of what Zimbabwe needs to revive its severely distressed economy, are reluctant to release aid without broad political reforms.
Tsvangirai said he had been told by Canadian Prime Minister Stephen Harper in a bilateral meeting at the WEF that the perception will remain "very negative" as long as Mugabe remains in power. Canadian government officials travelling with Harper were not immediately available for comment.
Many donors initially suspended aid over policy differences with Mugabe.
But Tsvangirai called on the West to be practical rather than theoretical.
"Come and make an assessment on the ground. Come and talk to Zimbabweans. How do they feel about the current political and economic situation in the country? And you'll be convinced that 85 percent support the inclusive government and its efforts," he said.
Despite his optimism, Tsvangirai acknowledged that he could not predict how Mugabe would behave. "Personally, I don't know what his intentions are."
Asked if Mugabe could seize full control of the country once again, Tsvangirai said: "I can't sit and predict that a coup will happen and that there will be a derailment of the project. All I am positive about is that so far this process is irreversible."
He said he meets with Mugabe once a week before Monday cabinet meetings, and that they walk into the meetings together.
Tsvangirai said it was difficult for him to deal with Mugabe given past acrimony.
He said he felt the veteran leader had in the past tried to "destroy" him but that was no longer the question.
"It is not that I will stand on top of the mountain and defend Mugabe's past, but I am talking about the country's future and this is the delicate moment to support the process that is taking place in Zimbabwe."
Tsvangirai said it may be as long as five years before the country can return to using the Zimbabwe dollar because it needs to rebuild its levels of industrial and agricultural production and its gold and foreign currency reserves.
The Zimbabwe dollar was destroyed by hyperinflation and replaced with multiple foreign currencies last year.
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