The year was 1966. By his side was an army of 30,000 fellow farmers from all across the country.
It took the Cork contingent 10 days to walk the 217 miles from Bantry to the capital.
By night they slept in cramped caravans set out at local marts in Tipperary, Laois and Kildare.
With the support of their families and communities, the defiant farmers, represented by more than 60 farm organisations at the time, demanded one thing from then minister of agriculture, Charles Haughey - recognition.
They remained there, sitting on the steps, for almost three weeks until their collective voice was finally heard.
"It was our duty as farmers to take part in the 'Long March'. We wanted recognition more than anything else. We wanted to stand up to the government and get things done, to ensure that we wouldn't be doubled crossed. We wanted a united voice for all farmers," said Mr Sullivan, a native of Bere Island, who was honoured for taking part in the 'Long March' at a special IFA 50-year commemoration last week.
Farmers were frustrated because of low prices for cattle, and milk and very limited scope to expand production because of poor export markets and the burden of paying rates.
"It rumbled on for months but we walked away with a new sense of purpose, a collective strength. Haughey got shifted and little by little things improved," said the 77-year-old dairy farmer who worked 30 acres of marginal land on the island at the time.
Although money wasn't great, the father of five said the social side of farming on the 4,900 acre island made up for low turnovers.
Farmers generally weren't in debt, land was rented relatively cheaply and, during the winter months, many worked on construction sites in London or spent time scallop fishing to gather extra cash to extend their holdings.
"You'd have no more than €20 in your pocket but you didn't owe anything. There were 70 milk suppliers going to the creamery on the island so the social side was very good," he said.
In fact, looking back, Mr Sullivan believes farmers were better off during the 60s, 70s and 80s, than they are today.
"Things have gotten good in some ways but for many farmers the reality is they are going down more than coming up.
"Times have changed a lot, we had little money but at least we owned the farms, the banks didn't," he said.
Coming from a farming family with a long history of emigration - long and short term - Mr Sullivan said it was much easier for his father and himself to work abroad and return home to farming.
Jackie emigrated to New York in 1949 with his mother and father. He was nine years old. They returned to Bere Island four years later during the Korean War. His parents were also worried about the emerging drug culture in NYC.
"We could emigrate to America or England but you could come back and farm again no problem.
"Now you can't do that because you have to have all sorts of Green Certs and everything else and that makes a big difference," he said.
"There are loads more complications and red tape for young farmer emigrants who want to come back with a family. The law is against them," said.
Although Mr Sullivan, who has grown his island farm from 30 to 100 acres, said joining the European Union in 1973 brought some vast and immediate improvements, he believes "we are in a very different EU today".
"When the Single Farm Payments came in it changed everything. It was paid out depending on stock, but since they changed it to paying on land there is no incentive, which is leading to disadvantaged areas being neglected and land abandoned," he said.
"There are more inspectors looking down your neck telling you to do. It's all about handouts rather than giving new incentives to work the land differently. It's crazy," he said.
He claims that farmers still need to have a second job outside the farm gate in order to supplement incomes.
"We joined a different Europe in 73, it's all about watchdogs today and Brussels is dictating everything we do on our farms," he said.
He is particularly concerned about the west coast of Ireland.
"It's getting worse all the time and you will have these areas going back to the hills. One time they were over grazed and over stocked. Now they are under grazed and under stocked and we can only burn them on EU calendar times because it effects the birds.
"It's time for us to seriously ask are the birds more important than people," he said.
Although two of his sons are currently involved in the family farm, Mr Sullivan is very concerned about agricultural opportunities on Bere Island for future generations.
The population of farmers on the island off the Beara Peninsula has dropped by 50pc since the historic 'Long March' of 1966.
"There are about 35 farmers on Bere Island now and I'm very worried about the future of farming on the island.
"It's costing too much to get stock on to it and to get them to the mart on the mainland, Kenmare is the nearest one," he said.
Hauling cattle from Bere Island to Kenmare takes about a day, with the stock losing about 20 kilos in transit.
The veteran campaigner is urging the Government and the Irish Farmers' Association to bring in new incentives that will encourage young farmers to work marginal lands.
"We have to do something in the disadvantaged areas with incentives for young people, there is no point in giving more money to the systems that are there, we need to create ways to get young farmers interested in farming in marginal areas.
"Leading by example is the best way of doing anything. We don't want disadvantaged landscapes to become hunting grounds for the rich," he said.
With world populations becoming increasingly urban and the recovery continuing to centre on life inside the M50, Mr Sullivan fears the country's rural fabric is slowly disappearing.
"On the whole of the Beara Peninsula right now there's only seven shops that sell groceries.People are living a lot longer now and what are they going to do if the small corner shop goes? There will be nothing left.
"There was 2,000 people on this island at one time but there is no more than 150 now and that is exactly what is happening all over the country in remote rural areas," he said.