'Window of opportunity'
Tsvangirai had refused to go to Swaziland for a meeting with Robert Mugabe, Zimbabwe's president, and four other regional leaders on October 20, in protest that he was only given emergency travel documents at the last minute.
Earlier in the week, the MDC had hinted Tsvangirai could also skip next week's summit in Harare.
The rival parties signed a deal one month ago for Mugabe to remain president and Tsvangirai to assume the new position of prime minister, but they have been unable to reach an agreement on who should control the key cabinet portfolios.
The power-sharing government is deadlocked over a disagreement on how ministries should be shared between the ruling Zanu-PF party of Mugabe, the MDC, and its splinter faction led by Arthur Mutambara.
The leaders of South Africa, Angola, Swaziland and Mozambique - who form the security committee of the Southern African Development Commission - are expected to help Zimbabwe's leaders break the deadlock.
Chamisa said the opposition hopes the summit will be able to break the impasse.
"Monday's platform gives us a special window of opportunity to state our compelling case for the equitable distribution of key ministries under the power sharing agreement," he said.