LGBT groups say the Pope's endorsement of same-sex civil unions under law is a "major step forward".
The pontiff has told a documentary that gay people have a "right to be in a family" and are "children of God".
But some Catholic officials say it "contradicts" the teachings of the Church.
Austen Ivereigh, a biographer of Pope Francis says the comments are of great significance.
"This will make, I think, a significant impact in many countries where gay people do not have basic civic rights and recognitions of their partnerships.
"[However], he is not in favour of opening the institution of marriage to gay people and he believes that gay marriage is an impossibility," Mr Ivereigh added.
Tánaiste Leo Varadkar welcomed the Pope's comments yesterday, tweeting: "Really significant and encouraging words from His Holiness."
