Ed's grandmother, also known as Nancy, died last Tuesday at the Castle Gardens Nursing Home in Enniscorthy, the Republic of Ireland. She will be laid to rest on Wednesday in St Patrick's Church, Monaseed, Gorey.
Mulligan's family remembered her as a "beloved wife of the late Bill and loving mother of Jim, Bill, Peter, Chris, John, MaryAnne, Bridget and the late Sally and sister of the late Thomas, Jim, May and Peggy".
The obituary added: "Deeply regretted by her loving sons, daughters, grandchildren, great grandchildren, sons-in-law, daughters-in-law, niece, nephews, relatives, friends and neighbours."
Mulligan was the inspiration behind Ed's 2017 song, Nancy Mulligan from his 2017 album Divide.
It tells the story of how Nancy, a Catholic from the Republic of Ireland, met Ed's late grandfather William Sheeran, a Protestant from Belfast, and fell in love during the Second World War.
Speaking of the story behind the song, Ed previously said: "They got engaged and no one turned up at their wedding. He stole all the gold teeth in his dental surgery and melted them down into a wedding ring, and they wore borrowed clothes to get married, and just basically have this kind of Romeo and Juliet romance, which is like the most romantic thing. So I thought I'd write a song about it and make it a jig."
Nancy and William went on to have eight children and 23 grandchildren.
Back in 2017, she was filmed listening to Ed's song for the first time and told RTE News: "I'll never think of [Ed] as being famous, I have to say. He's exactly the same as he always is when he visits. And it's very rare because he's always working and when you think he was working from the age of 14, you'd have to feel sorry for him, you know he's so tired but he loved it."