And the legendary tv anchor revealed that she had her 'waterproof mascara' at the ready in anticipation of shedding some tears.
"It was a wonderful honour for me to play a part in the ceremony, and of course, I shed a tear or two," she told the Irish Daily Star.
"But it was also a very joyous occasion because tere's something very rare and wonderful about two people making a commitment to each other for the rest of their lives."
The RTE newsreader and his former colleague arrived in style at the wedding venue in Ballymacgarvey village, Co Meath, yesterday.
The pair pulled up to the venue in a black Rolls-Royce holding hands and smiling widely before dashing through the doors.
After 10 years together, Mac Grianna and his partner Terry Gill said their 'I dos' in front of 150 close friends and family members.
Several of Mac Grianna's former 'Masterchef' competitors including Yvonne Keating, Tracy Piggott and Maia Dunphy attended the humanist ceremony. And there were plenty of familiar faces from the RTE newsroom with Eileen Dunne, Michael Murphy, Kate Egan and Teresa Mannion taking their seats.
Gill walked up the aisle with his mother Eva Gill while musicians Moya Brennan and harpist Cormac De Barra performed a selection of traditional Irish ballads.
Mac Grianna followed with legendary broadcaster Doyle by his side. Doyle joked that she felt like Mrs Bennett from Jane Austen's classic novel 'Pride and Prejudice' in the run-up to the wedding.
"It's weddings, weddings, weddings at the moment. All I seem to be talking and thinking about are weddings these days," she said, referring to both Mac Grianna's nuptials and the wedding of her partner Dan McGrattan's son which took place last Friday.
Mac Grianna chose Doyle to give him away as he has known her for "donkey's years".
"From the very beginning Anne always looked out for me," he said.
"She has watched and guided me along the way and at key junctions in my life – she has always been there. She has been a major influence on me. She's a one-off."
The crowd erupted into applause when the ceremony drew to a close and the couple were beaming as guests congratulated them.
The pair met in a Dublin pub The Front Lounge 10 years ago when Mac Grianna was enjoying a "liquid lunch" with some of his colleagues and instantly hit it off.
Mac Grianna and Gill will travel to the UK in the coming weeks to legally marry. Mac Grianna has spoken about the issue of marriage equality in the past.
He said: "It's simply a question of equality. All of my brothers and sisters are married and I don't see any difference as to why I shouldn't be allowed that too. I'm not prepared to take a lesser status."
The couple will head off on honeymoon in the coming days. Gill proposed to Mac Grianna when he returned from the 'Masterchef' final in Dubai last year.