Republicans of all shades are expected to converge on Strabane at the weekend for the first March for Irish Unity.
Organisers say the parade, which thousands of people are expected to attend, is the start of an Ireland-wide movement that "cannot be stopped".
Unionists were invited to "discuss their place in a united Ireland", but one called the march an exercise in "chasing fantasy".
Billed as a "peaceful, anti- sectarian, grassroots gathering with a view to mobilising collective voices for a new and united Ireland", the parade has the backing of a number of republican groupings, including Sinn Fein and the Irish Republican Socialist Party.
Independent Strabane councillor Paul Gallagher said the parade would be "a platform for the communities in the north-west of Ireland to express their desire for a united Ireland".
"This march is about Irish unity," he added.
"It's a non-party, non-political, non-sectarian, peaceful march.
"No political banners are allowed - just the national flag - and there will be no marching bands.
"This is just a community that wants to express its desires for a united Ireland without putting a political tag on it.
"This march and movement is going to move across Ireland.
"(It will) leave a legacy while engaging in various meetings, community centres and places of work.
"We want to engage people around what their vision of a united Ireland should be.
"The movement is starting in Strabane and we will take it around Ireland.
"It has nothing to do with the Good Friday Agreement, nor border polls.
"It is just about people expressing their desires over living in a united Ireland."
Mr Gallagher said a range of speakers would take to the stage, from trade union and Irish language campaigners to people from a sporting background and the well-known musician Frances Black.
He also stressed there would be no political speakers.
"There will be various shades of republicanism there," Mr Gallagher said.
"It will be a wide range of republicans who don't see eye to eye on everything but share the common issue around unity and are prepared to put other things aside and come together around unity.
"This march is not controversial. For decades there has been a desire for Irish unity, and that desire has not stopped. There is nothing controversial about wanting Ireland to be united.
"The momentum that is gathering for unity, nothing will stop it."
Mr Gallagher said that unionists were "most welcome" to attend Sunday's march and other engagement events planned across Ireland in the coming months.
"People from the Protestant, unionist and loyalist community are more than welcome to come and engage, and are engaging, about where their place is among all this," he added.
"They have every right to ask (about) that. There will be other venues for engagement and I would welcome that. This has to be inclusive."
The DUP's Tom Buchanan, who is standing as the party's Westminster candidate in the area, said "chasing united Ireland fantasies will not fix Northern Ireland's problems".
"Northern Ireland's future is best served inside the United Kingdom for economic, social, cultural and historic reasons," he added.
"A border poll would be divisive and would take this community backwards.
"Our focus should be on restoring devolution and ensuring people who live here have all the services they require.
"Chasing united Ireland fantasies will not fix our roads, provide better healthcare or support children in our classrooms."
A spokesperson for the PSNI said that the "march will be policed appropriately and proportionately".
The March for Irish Unity will take place on Sunday.
It will begin at 1pm at the Diamond in Lifford before marching into Abercorn Square in Strabane.