Here’s what you need to know:
Long time coming
Mujuru said the pact had taken “more than six months” to come up with. Critics of President Robert Mugabe have been saying for some time now that a coalition is the only hope Zimbabweans have of getting Mugabe voted out of power in 2018.
Tsvangirai and his MDC came closest to unseating Mugabe in 2008, when the longtime leader lost the first round of presidential elections to the opposition leader.
But Tsvangirai’s years as prime minister in a coalition government saw him losing some of his popularity. He’s still struggling to claw it back.
Mujuru in the meantime saw some of her ex-ZANU-PF allies, notably Didymus Mutasa, depart in a huff in February.
Zimbabweans on social media – at least, those who don’t support Mugabe – have been largely welcoming of the news.
“Good move on a historic day. Zimbabweans lets work together and remove ZANU-PF,” wrote Nashe Mukoki on the MDC’s Facebook page.
“Well done well done” posted Jabulani Mandiveyi.
Not using the word coalition – for now
Neither Tsvangirai nor Mujuru is using the word coalition to describe this stage of the agreement. The exact term being used is “pre-election alliance.”
(Tsvangirai talked about the alliance being the first step towards the formation of a “coalition government”).
The editor of the pro-Mugabe Herald newspaper, Caesar Zvayi, DID use the word coalition when he asked on Twitter whether Wednesday’s news was a “gamechanger or “coalition of zeroes?”
While the MDC almost certainly still has the biggest anti-Mugabe following in Zimbabwe, there are many other opposition parties and figures who could at this point dilute a Tsvangirai-Mujuru vote.
This hasn’t been spelled out. The privately-owned NewsDay suggested earlier this month that Mujuru had hinted Tsvangirai could lead a coalition. .
Mujuru said at the public signing ceremony on Wednesday that she would lead a “political committee” while Tsvangirai would lead a “diplomatic committee.”