The unassuming founder and director of Mary's Meals is uncomfortable with self-promotion and prefers instead to talk about the humanitarian crisis his army of 10,000 volunteers is trying to cope with.
He has seen the appalling living conditions suffered by Haitians, and Somalian women walking hundreds of kilometres in a desperate search for food. "Haiti has been among the worst situations I've encountered ... also the Somalia famine when we were taking in food from Malawi. In the camps there, I talked to women who had watched some of their children die on the way."
He struggles too with disturbing memories from the aftermath in Sri Lanka of the Indian Ocean tsunami and "horror of parents looking for the bodies of their own children".
MacFarlane-Barrow's charity career began by accident in 1992.
After watching graphic television reports of refugee camps during the Bosnian War, Magnus and his brother Fergus - both devout Catholics - decided to take aid to the region by driving a Land Rover filled with clothes, food, medicine and toiletries.
Magnus, 24 at the time, and Fergus, 25, were drawn to the conflict because a decade earlier both made a life-changing pilgrimage to Medjugorje in Bosnia-Herzegovina, a village famed for apparitions of the Virgin Mary. Hundreds of thousands of Catholics visit the place each year.
The brothers asked local people to assist them and after they returned from their first trip to Bosnia they found donations just kept coming in, filling their parents' shed with supplies. McFarlane-Barrow was so affected by what he saw in Bosnia that he decided to devote a year of his life to driving more aid into the country despite the obvious dangers of operating in a war zone.
By the end of 1993, he'd set up a charity called Scottish International Relief (SIR) and instead of returning to salmon farming, McFarlane-Barrow became its first full-time member of staff which set his life on a different path.
"At first I didn't realise I was making choices that would have such an impact on the rest of my life - it didn't seem like a momentous decision. I thought I was making decisions about the next few months of my life and then it unfolded bit by bit. And that was before I was married with children [he has seven] - later in life it would have been much harder to leave a secure job to work unpaid driving trucks into Bosnia," he says.
SIR expanded and began working in Romania where it built homes for abandoned children.
In Liberia, the charity helped returning refugees by setting up mobile clinics and MacFarlane-Barrow continued to deliver material aid to both Croatia and Bosnia while funding some new projects.
In 2002, Mary's Meals was born when MacFarlane-Barrow was delivering emergency aid during a famine in Malawi. He recalls meeting a young boy called Edward whose father had died and his mother, Emma, was dying of Aids. She was lying on the floor of her hut surrounded by her six young children. She said all that was left was to pray for her children with the hope that someone might care for them after she died. When MacFarlane-Barrow asked Edward what he hoped for in life, the boy replied: "To have enough food to eat and to go to school one day."
It was a defining moment that has stayed with MacFarlane-Barrow ever since. "This, and other encounters with children missing school because of hunger, left me convinced that the provision of a daily meal in a place of education would meet both the immediate need of the hungry child and - at the same time - draw them into the classroom, enabling them to gain an education that could be their ladder out of poverty."
From 2002 to 2012, Mary's Meals was just one campaign of SIR but it became MacFarlane-Barrow's sole focus after he realised its ethos was the best approach to helping children survive abject poverty. Thus in 2012, SIR officially changed to become Mary's Meals.
The ethos of Mary's Meals is simple: children are encouraged to attend school and if they do so they are fed a nutritious meal.
"By providing one good meal to hungry children every schoolday we are filling their empty bellies so they have the energy and opportunity to learn - and this can be their escape route out of poverty in later life," he says.
The charity is now well-established around the world with projects in five continents. There are seven in Africa, four in Asia, three in Europe and one in Ecuador, South America. Hundreds of children are also fed daily in the Caribbean where a project in a slum area of the Haitian capital Port Au Prince supports one of the most impoverished communities anywhere in the world.
"Things in much of Haiti are still dire - just as they were before the earthquake. There are so many hungry, malnourished children there. It makes me sad that the attention and global interest in the aftermath of that horrible disaster seems to have dissipated. I hear people say Haiti is a hopeless case - which it certainly isn't. Mary's Meals is helping thousands of the poorest children attend school there, and those children alone give plenty of reasons to be hopeful about the future. Often in these situations, I have witnessed the incredible strength, dignity and goodness of people, who even in the midst of such horrors continue to help those around them."
Mary's Meals goes from strength to strength and a powerful new documentary about its work was premiered in some 300 different locations across the world. The film Child 31 has been endorsed by high-profile Scots including actor Gerard Butler, former British Prime Minister, Gordon Brown, and pop singer Annie Lennox who said the film highlights the "unimaginable challenges faced by children living in poverty".
While Mary's Meals is now global, MacFarlane-Barrow is determined his charity should retain its original values and he says there are still some 300 million chronically hungry children in the world and around 61 million not in education.
"I am not qualified to do this work and have had no formal training so I've been on a very steep learning curve for last 20 years - and I am still on it. The organisational change required as we grow and set up in many different countries can be challenging, and the travel is challenging to balance with my family life. But our vision is that every child should receive one good meal every day in their place of education. I believe that is possible in this world of plenty."
