LIAM Neeson and Graham Norton are calling for the introduction of same-sex marriage in Northern Ireland.
Snow Patrol singer Gary Lightbody and The Fall star Bronagh Waugh have also lent their voices to the campaign.
Northern Ireland remains the only part of the UK where same-sex marriage is illegal.
A protest will be held in Belfast city centre on Saturday, amid an ongoing political dispute on the region's ban on same-sex marriages.
The issue is one of a number of major stumbling blocks in the ongoing negotiations to restore power-sharing at Stormont between Sinn Féin and the DUP.
Amnesty International, who is organising the Love Equality march, released statements from the celebrity backers.
"We've had enough of a history in our society in Northern Ireland of discrimination, mistrust and hatred," said Ballymena-born Neeson.
"Yet, we're also an open-hearted, welcoming and terrific people. Let us show that to the world by treating gay, lesbian and transgender peoples as our brothers and sisters and allowing them to marry, if they so wish.
"By joining the rest of Ireland and other western countries in celebrating equality we can also attract more investment to our province.
"We have shown the world how we can affect a peace accord when many thought it impossible.
"We must act on this and welcome all members of society through civil marriages, while still keeping our Christian values. Love, is love, is love.”
The DUP has previously rejected claims it is homophobic, insisting it is instead protecting the “traditional definition” of marriage.
Chat show presenter Graham Norton said the historic referendum that legalised gay marriage in the Republic of Ireland was a “proud gay day”.
"It moved me to tears because it was something I never dared hope would happen," he said. "My own mother was from Northern Ireland, so of course I have a huge affection for the place and its people.
"I know it is hugely frustrating for gay people there that it is the last part of these islands still without marriage equality.
"Especially when there is such overwhelming support for it among the public.”
Snow Patrol singer Gary Lightbody has also lent his voice to the campaign. (Picture: Getty)He added: "My heart is with all those who will be marching for civil marriage equality in Belfast on July 1. Go you."
Gay British comedian Stephen Fry, who famously portrayed Irish poet Oscar Wilde, said: “I send my love to the people of Northern Ireland. Especially all those couples striving and marching for the right to marry and have their love celebrated.”
Fry, who married comedian Elliott Spencer in January 2015, added: “Why should loving couples in Northern Ireland be denied this chance of happiness, of equality, enjoyed by people in every other part of these wonderful islands? It doesn't make sense.
"Simply put, I want the same joy that I have found to be available to people in Northern Ireland.”
Co. Down-born Snow Patrol singer Gary Lightbody added: "Two years ago, I marched with 20,000 fellow Northern Ireland citizens for marriage equality. It was a beautiful day of hope, joy and solidarity and I was so proud to be from 'Norn Iron'.
"Two years on and somehow - defying reason given it's the will of the people - we still do not have marriage equality in Northern Ireland.
"We're in the States making our new album, so we can't be there in person to march again for marriage equality, for togetherness, for reason and for love. Everyone in Snow Patrol will be there in spirit.
"I hope the day is as special, even more special, than two years ago and I hope those that should listen to the will of the people do listen. Surely, they must. Surely. One love."
Coleraine-born actress Bronagh Waugh will host the demonstration rally at Belfast City Hall.
"With the spotlight being shone on Northern Ireland at the minute, now is our chance to really step up our campaigning a gear and give Northern Ireland what it so clearly wants and deserves, finally - equal marriage," she said.
"This is a human rights issue. We will not rest until everyone in Northern Ireland has equal rights like the rest of the UK."
Singer Neil Hannon of The Divine Comedy, who was born in Co. Derry, also backed the campaign.
"I am 100 per cent behind the fight for marriage equality in Northern Ireland," he said. "The inexorable march towards equality and acceptance of all sexual orientations and genders in recent decades has been a joy to behold.
"Many brave people have put themselves in the firing line in pursuit of the dream.
"Thankfully they are now claiming victory after victory across Europe and the wider world. I fervently hope for the same in our little part of that world.
"In the immortal words of Lenny Kravitz - Let Love Rule. Have a great day."
