Mr Tsvangirai, a former trade union leader, stood against President Robert Mugabe in 2008 but agreed to enter a power-sharing arrangement with his rival in order to avoid civil unrest in a run-off.
The pair are due to have a rematch next year after a referendum on a proposed new constitution in a couple of months.
President Mugabe, now aged 88, has held power for 32 years.
Mr Key paid tribute to Mr Tsvangirai's "courage" in advancing democracy in Zimbabwe. He said the pair discussed the possibility of sending officials to New Zealand from Zimbabwe, of being able to help economic development with agricultural expertise and possibly giving New Zealand's aid more directly.
"Obviously we care a lot about the plight of every day Zimbabweans."
Mr Tsvangirai said the $4 million aid to Unicef for Zimbabwe had been spent on printing textbooks for primary and secondary students.
He said his aim was not just to stabilise the economy but to grow the economy.
"In order to do that ... we would definitely implore the international business community to come to Zimbabwe to look at Zimbabwe's investment potential in mining, tourism, in agriculture and other sectors.
He had a meeting with Business New Zealand today in Wellington.
While acknowledging the violence that he and others had been subjected to, he said: "We are in a phase in which we have to rebuild the country and move forward."
"We need to open a new chapter ... revenge is not an issue ... what we should do is reconciliation, rebuilding and reconstruction."
He said his relationship with Mr Mugabe had been so acrimonious it polarised society.
"It has evolved from that relationship to a relationship where we do business for the sake of the country. It has improved. We respect each other but we differ, respectively."
Mr Tsvangirai said that in 2008 Mr Mugabe had been on the point of giving up but "was prevented from doing so by the military."
Asked whether he believed Mr Mugabe would accept the result of the next vote, he said, "I don't see any reason why he would plunge the country again into another dispute. I think he is committed for his own legacy and the legacy of the country to move forward in a stable way. He has to accept the result if it is conducted in a free and fair manner."
Asked about media freedom in Zimbabwe he said that he was not happy with the state media. "The state media has been at the forefront ... of promoting hate speech."
"You media, you always want to sensationalise the truth," Mr Tsvangirai said.
Mr Key added: "Ain't that the truth."
NZ SANCTIONS AGAINST ZIMBABWE
Travel ban against President Robert Mugabe and 334 close associates of his regime.
Restrictions on sporting teams from Zimbabwe.
Suspension of visitor visa waiver for Zimbabwe.