Either Rebecca Long-Bailey, Sir Keir Starmer or Lisa Nandy will replace outgoing Mr Corbyn.
In the race to succeed Mr Watson, who resigned ahead of the December election, is Angela Rayner, Ian Murray, Richard Burgon, Dawn Butler, and Dr Rosena Allin Khan.
The winners will be announced in an email to members, it is understood, after a special leadership conference was cancelled due to coronavirus.
There'll also be an acceptance speech in the form of a video, which will be recorded by each candidate ahead of the result.
The winners will be revealed Saturday morning.
In the leadership election Sir Keir has long been the favourite, while Ms Long-Bailey has been viewed as Mr Corbyn's continuity candidate and Ms Nandy the outsider.
In the deputy leadership contest, shadow education secretary Ms Rayner is the favourite to win.
Earlier this week, Ms Long-Bailey told of the "bizarre" prospect that she'll have to pre-record a victory speech.
She revealed it was a logistical move, that each candidate had been asked to record something as a way to "deal with these strange times" brought about by the coronavirus.
After the polls closed in the election, Sir Keir tweeted thanks to all his supporters.
He added: "I honestly believe that we have come out of the other end of this contest as a better party: more united and ready to build another future."
Ms Nandy did the same, writing thanks to "everyone who’s voted in the contest so far. Very proud to have your support."
Among those eligible to vote in the contest were 114,000 new members who joined since the election, plus almost 15,000 "registered supporters" who paid £25 for the ability to vote.
On top of that, Labour had 485,000 members - as of July 2019 - who would have been able to vote if they remained in the party when voting began on February 23.
The winner is selected using a preferential voting system.
That means voters pick their favourite, then their second and third preferences.
If there is no overall winner, the candidate who came last is removed and the second preference of people who voted for them as their favourite is redistributed so a majority can be found.