Both Mr Tsvangirai (l) and Mr Mugabe claim to have won this year's elections
Zimbabwe's President Robert Mugabe is to retain control of the army and chair cabinet meetings, according to leaks of Thursday's power-sharing deal.
South African President Thabo Mbeki said Mr Mugabe had agreed to share power with Morgan Tsvangirai but said details would be released on Monday.
Mr Tsvangirai will control the police force and chair a new council of ministers, the sources say.
The deal followed seven weeks of talks and this year's election violence.
Mr Mugabe has yet to comment on the agreement, brokered by South Africa's leader.
BBC News is banned in Zimbabwe, but a BBC correspondent inside the country says MDC supporters are not rejoicing on the streets, nor are Zanu-PF backers protesting.
Instead a silent optimism prevails - and after so many false dawns, Zimbabwe is holding its breath, our correspondent says.
Heads armed forces
Zanu-PF has 15 ministers
Chairs council of ministers
Controls police force
MDC has 16 ministers - 3 from smaller faction
International donors have said they would resume financial aid for Zimbabwe's collapsing economy if Mr Tsvangirai's Movement for Democratic Change (MDC) is given a genuine share of power.
The EU said it would "evaluate the situation" at a foreign ministers' meeting on Monday.
BBC world affairs correspondent Adam Mynott says the agreement appears to give Mr Mugabe and Mr Tsvangirai roughly equal shares of power.
In cabinet, Mr Tsvangirai's MDC and another MDC faction will together have 16 seats, while Mr Mugabe's Zanu-PF will have the remaining 15.
Mr Mugabe will control the armed forces, while Mr Tsvangirai will be in charge of the police.
Our correspondent says the devil will lie in the detail and in the ability of the two men and the power blocks under them to wield genuine authority.
Mbeki hails deal
Work on finalising the agreement will continue over the weekend. Some opposition MDC voices have already called the deal a climb-down, although others have said it is the best available.
MDC chairman and Zimbabwe's parliamentary speaker Lovemore Moyo told the BBC that although his party was pleased with the deal, it had been a compromise.
Zimbabweans share views on deal
"We wanted a titular head of state with an executive prime minister but that did not happen," he said.
"So what we got at the end of the day perhaps was probably nearly a sister-sister power-sharing, so I'm saying it's not exactly initially what we wanted."
Negotiations started at the end of July, but stalled over the allocation of executive power between Mr Mugabe and Mr Tsvangirai - bitter rivals for a decade.
The breakthrough came after the last four days of talks in the Zimbabwean capital, Harare.
Mr Tsvangirai was first to announce the breakthrough, telling reporters on Thursday simply: "We've got a deal."
Later, Mr Mbeki told a news conference the two sides had agreed to form an inclusive government.
He said: "I am absolutely certain that the leadership of Zimbabwe is committed to implementing these agreements."
The deal would be signed at a ceremony in Harare attended by African leaders, he said.
Zimbabwe's envoy to the UN, Boniface Chidyausiku, told the BBC that the deal was a "triumph for African diplomacy".
The UN special representative on Zimbabwe, Haile Menkerios, said the announcement marked a way forward that all sides could live with.
HAVE YOUR SAY
This deal will work if outsiders stop prescribing to Zimbabweans what is good or not good for them
Britain's Foreign Office said it was following the situation closely, adding that "our concern is the welfare of the Zimbabwean people".
Zimbabwe has the fastest shrinking economy in the world with annual inflation of more than 11,000,000%.
Mr Mugabe, in power since independence from Britain in 1980, won a controversial presidential run-off election in June.
He ran unopposed after Mr Tsvangirai withdrew, claiming the MDC was the target of state-sponsored violence.
In the first round of the presidential election in March, Mr Tsvangirai gained more votes than Mr Mugabe, but official results say he did not pass the 50% threshold for outright victory.