DUP leader Arlene Foster will attack Jeremy Corbyn as beyond the "political Pale" because of his past support for Irish republicans in a speech today.
She is expected to attack the Labour leader's democratic credentials and voice support for his Conservative rival.
Mr Corbyn has said he wanted the violence in Northern Ireland to stop but refused to single out the IRA for condemnation during recent interviews.
The former First Minister will say: "While Theresa May is well within the political mainstream and has proven herself to be a solid and reliable unionist, Jeremy Corbyn is beyond the political Pale.
"It is hard to take seriously the democratic credentials of a man who was so close to the political representatives of the IRA at the height of the Troubles.
"It is hard to see much good coming for the Labour Party from the coming election except the replacement of their leader." Mr Corbyn and shadow chancellor John McDonnell have faced scrutiny over their association with republicans.
Before the IRA ceasefire they controversially met Sinn Fein a number of times in Westminster during the 1990s.
Mr McDonnell has apologised for comments he made praising the IRA's "bravery" in 2003.
After becoming Labour leader in 2015, Mr Corbyn defended reaching out to republicans during the Troubles - insisting he "wanted the violence to stop".
At lunchtime, Mrs Foster will address a meeting of the pro-Brexit Bruges Group in Mayfair on Brexit and the Union.
Although Northern Ireland voted by 56% to 44% in favour of Remain in last June's referendum, the DUP campaigned for an exit.
She will say: "Who could deny that the situation of Northern Ireland within the UK, and indeed Ireland within the EU, will face different challenges from other areas affected by the UK's EU exit and will require unique and tailored solutions?
"However, I do not believe that a circular argument about some ill-defined and ill-conceived so-called special status for Northern Ireland is helpful: indeed, it is more likely to be counter-productive."
At the same time, the DUP leader claims she will be flexible over Brexit arrangements.
"I am more interested in getting the best deal for Northern Ireland and the UK as a whole than I am in some doctrine or dogma. By far the best way to achieve this is to get a Stormont Executive up and running as quickly as possible."
Mrs Foster also believes there is "reason for optimism" over how Northern Ireland will emerge after the UK quits the European Union.
"During the referendum campaign and since, some of those who advocated 'Remain' have argued that the UK's departure from the EU will result in a hard border on the island of Ireland," she will say. "I know of no one who wishes that to be the case."
Mrs Foster will say that "by far the most important Union for the people of Northern Ireland economically is the Union with Great Britain".
But she will add that it "need not come at the cost of accepting the economic and cultural ties that cross the border".
"For once, there need not be a winner and a loser," she will tell an audience at The Lansdowne Club. "The Republic of Ireland needs a good outcome to these negotiations every bit as much as we do and I believe there is a shared objective between the UK and the Republic to get the right deal."