While Labour's Jeremy Corbyn has persistently called for a general election in recent years, and particularly since Boris Johnson became Prime Minister - accusing him of having no electoral mandate - he quickly changed his mind when the PM agreed there should be a snap vote last week, deciding that now was not the time.
Mr Watson will declare: "Boris Johnson has already conceded that the Brexit crisis can only be solved by the British people".
Mr Corbyn will meet unions later.
Opposition leaders have not supported the votes, which needed the backing of two-thirds of MPs, because they fear an election could be used to force through a no-deal Brexit.
The discontent towards the measures taken by the Prime Minister started to show on the first day, when Phillip Lee, a member of the Conservative Party, walked to the Liberal Democrat Party as Johnson spoke, giving the opposition the majority of MPs with 320 members to the the government's 319.
In a speech on Wednesday in London, Mr Watson will say a single-issue Brexit election may not break the deadlock in Parliament - something only a second referendum can achieve with certainty.
"The only way to break the Brexit deadlock once and for all is a public vote in a referendum", he will say.
But once it has done that, MPs should focus on securing a referendum before an election.
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It took some time for those tendencies to show themselves on Wednesday, but once they did Andreescu was her normal ferocious self. I'm sure off the court we are still friends. "I think it gives me extra motivation to just keep striving and keep doing well".
In his own speech in Brighton on Tuesday, Mr Corbyn said Labour would commit to a public vote during the next general election campaign "with a credible option to Leave and the option to Remain".
Labour must prioritise reversing Brexit through another referendum, over winning power in a general election, its deputy leader Tom Watson is to say.
"But there at some point comes a position - and we are quite much earlier it now, effectively into the fourth year given that the referendum - when situations are so modified, when so a great deal new info has emerged that we failed to have in 2016, when so many people today experience otherwise to how they felt then, that you have to say, no, that a long time-aged plebiscite is no for a longer period a valid basis on which to acquire these types of a momentous conclusion about the potential of the United Kingdom".
'No one can trust the word of a prime minister who is threatening to break the law to force through no-deal, ' Corbyn stressed, after recalling that an exit from the European Union on bad terms would result in job losses, trigger food price increases and cause a shortage of medicines in the UK.
"Nothing could be further from the truth". However, this new legislation obliges the prime minister to ask E.U. members for an extended period of 3 months to exit the union, unless Parliament approves a deal or consents to a no-deal Brexit by October 19th.
"Brexit will of course be a crucial issue at this election".
"They just want us to take an unequivocal position that whatever happens we'll fight to remain, and to sound like we mean it". "We have to draw a line under the wasted years of Tory rule and failed negotiations".