The agreement was in line with the Southern African Development Community (SADC) process.
The two leaders met at Tuynhuys in Cape Town and Zuma said he was concerned with the situation in Zimbabwe.
"Zimbabwe should not be allowed to slide back into instability," he said.
Tsvangirai briefed Zuma on recent developments in Zimbabwe, and indicated his intention to brief other leaders as well.
On Tuesday an aide to Tsvangirai told a Wits University lecture that Zimbabwe’s government of national unity would continue unless constitutional reform was derailed.
"If Zanu-PF derailed the constitutional [reform] then there would be no reason to stay in government," minister of state in the prime minister’s office Gordon Moyo said.
Despite criticism of the government of national unity (GNU), Moyo said it still had the support of members of Tsvangirai’s party, the Movement for Democratic Change (MDC).
Tsvangirai has reportedly met with the leaders of the SADC and appealed for their help in dealing with the impasse in the GNU.
"We are expecting them to put pressure on Zanu-PF," Moyo said.
In the past week, the MDC had "disengaged" from government following the arrest of MDC member of Parliament Roy Bennett.
Moyo, however, said his party would not withdraw from the government.
"Our intention is not to pull out of the government, because we won the election." — Sapa