The rally comes as an EU delegation was wrapping up a two-day visit to Zimbabwe, the first in seven years, following rare talks Saturday with long-ruling President Robert Mugabe and Tsvangirai.
Tsvangirai and Mugabe formed a power-sharing government in February, but remain bitterly split over appointments to key posts and claims of official persecution by members of the premier’s Movement for Democratic Change (MDC).
But for most Zimbabweans, life has improved this year after the government abandoned the local currency, worthless after years of hyperinflation, and eased price controls that have allowed shops to restock food and businesses to slowly resume operations.
"I know that taking the step to join this government was not easy," Tsvangirai told his party’s top leaders late Saturday.
"But it is a step in the right direction. We remain committed to the ideals of real change, and real change will come to Zimbabwe," he said.
On Sunday, thousands of MDC supporters were expected to hear Tsvangirai speak in a stadium in Bulawayo, Zimbabwe’s second city and bastion of support for the party.
They will also remember the 300 people who the party says have died during a decade of political violence targetted mainly at the MDC by pro-Mugabe militants.
The MDC was formed on September 11, 1999 after a coalition of rights groups, churches and civic society agreed to launch an opposition party to challenge Mugabe’s rule.
The party made rapid electoral gains in its first year, finally seizing a parliamentary majority in last year’s elections, when Tsvangirai also defeated Mugabe in a first-round presidential vote.
MDC chairman Lovemore Moyo said the past decade had brought untold suffering to its members.
Tsvangirai pulled out of the runoff, citing a wave of deadly attacks on his supporters that MDC says left more than 200 dead. Former South African president Thabo Mbeki mediated a unity accord one year ago that eventually led to the power-sharing government.
"The whole nation meets here in Bulawayo, to celebrate ten years of our democratic struggle, ten years of courage, ten years of dedication, ten years of untold suffering in the hands of the Mugabe regime and ten years of hard work," Moyo told party delegates late Saturday.
"We are grateful for the support that you have rendered to us during the good and difficult times of our democratic struggle and we are indeed happy that you have understood our cause."
Moyo said the party must now prepare for the next general elections, but did not say when they might be held.
The unity government is meant as a transitional authority to oversee the writing of a new constitution that will guide the nation to fresh elections.
The EU delegation said after its talks with the nation’s leaders that the process needed to include human rights protections, media freedom and other political reforms.
Tsvangirai has launched a major effort at normalising ties with western nations, who have imposed sanctions on Mugabe and his inner circle following 2002 elections that western observers and local poll monitors said were flawed.
Mugabe regularly lashes out over the sanctions, which include a travel ban and asset freeze on his family and top aides.
The EU team on Sunday planned to visit clean water projects aimed at preventing a new outbreak of cholera, which has killed more than 4,200 people since August 2008. They were set to leave Zimbabwe later in the day.