Maryanne, 48, and Tommy Pilling, 62, from South-End-on-Sea, Essex will toast the anniversary of their big day alongside loved ones at a party in their garden.
Tommy proposed after 18 months of dating, using a toy ring from a vending machine - but not before he'd asked Maryanne's mum for her blessing.
The pair have so far managed to live independently but Tommy is now facing a heart-breaking struggle with dementia, which brings a new set of challenges.
Despite those hurdles, the pair love one another to bits and "never argue".
Today, Maryanne helps care for her husband Tommy, 62, alongside her sister, Lindi Newman, 32 and mum Linda, 69.
Talking about the couple, sister Lindi, who works as a full time carer, said: "To the best of our knowledge, they're now the longest living married couple with Down's Syndrome.
"The fact that they're still living independently and are doing great together, it's amazing.
"These last few years have been substantially harder and Maryanne does get upset - Maryanne had dreamt of a big white wedding since she was a little girl, and their relationship is one that has always been full of love.
"But Tommy doesn't sleep, and whilst his memory isn't that bad, he does get mood swings and it's clear, his health is declining rapidly.
"But their family is all round them - Tommy lost his family quite young and we took him in 30 years ago now.
"He's part of the family and their relationship - it's absolutely wonderful."
The couple even have their own Facebook page, which is full of pictures and details of their 30-year relationship, and has racked up over 60K likes.
Lindi said: "Maryanne doesn't remember a life before Tommy.
"The day she met him, she had the biggest smile on her face and she couldn't stop talking about him.
"With their 25th wedding anniversary coming up, we're planning a big party in July.
"Whilst Maryanne and Tommy might not have the concept of what an achievement it is, to them it's just their relationship, to us it's just absolutely brilliant."
Talking about her relationship with Tommy, Maryanne said: "My wedding was the best day of my life. I was shocked when Tommy proposed but I didn't have to think twice about saying yes.
"Tommy and I never argue. I love my husband very much. He is my best friend."
We're not crying, you're crying. Congratulations, Tommy and Maryanne!
Featured Image Credit: Caters
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