Former rebels prepare to fly the flag of independence from Khartoum as South Sudan becomes world's newest nation

The freedom suit is tan, single-breasted and has three buttons. It hangs in Charles Mamur's tent, covered by a black bag to protect it from the dust that blows in from the dirt streets of South Sudan's capital, Juba.

Mamur bought the suit two years ago for about £50 but he has never worn it. He was keeping it for a special occasion, a time that he had dreamed of since the day nearly 50 years ago when, as a 10-year-old boy, he took up arms against the Arab government in Khartoum in the north.

"I never believed that the moment of freedom would come," Mamur, 58, said this week, unzipping the bag to show off his suit, as well as the yellow tie and black shoes he picked to go with it. "But I wanted to be well dressed if it did."

The moment has now arrived. At around noon on Saturday in the swelter of Juba, a besuited Mamur will be among tens of thousands of South Sudanese and foreign dignitaries, including the British foreign secretary, William Hague, and the UN secretary general, Ban Ki-moon, who will watch as the flag of Sudan is lowered. Then, a giant South Sudan flag, six metres by four metres, will be raised on a 32-metre electronically operated flagpole that was installed this week by Chinese contractors who claim it is the tallest on the continent.

Six years after the end of Africa's longest-running civil war – and one of its deadliest – its largest country will be officially split in two. The Arab-dominated north under President Omar al-Bashir will remain Sudan, only with much less territory and oil. The ethnically African, non-Muslim south, governed by former rebel Salva Kiir, will become the 193rd country to join the United Nations – the Republic of South Sudan.

The excitement and anticipation here in the buildup to independence is hard to overstate, eclipsing even the joy that accompanied the January referendum that saw 99% of voters choose secession over unity.

Every South Sudanese knows that the new state, among the least developed countries on earth, faces immense challenges. But those are challenges for tomorrow, and thereafter. For now, for a people who have suffered so much, for so long, it's a time of celebration.

"This is the day we have all been waiting for," said Luka Loro, a 35-year-old sanitary officer. "Our forefathers fought for this since 1955, and now we have achieved it."

He was supervising the cleanup of the field where the ceremony will occur, part of a huge operation to spruce up Juba, which has grown from little more than a village to a booming city over the past few years.

Small armies of women with brooms and T-shirts that declare "Keep Juba Clean and Green" are trying to defy nature by sweeping dust off the tarred streets.

The new dancing fountain at one of the city's main roundabouts glows pink, blue, green, yellow, red and white as it rises and falls.

Inside homes, people are installing satellite dishes to watch the celebrations on television, and practising the new national anthem.

"We are singing in the kitchen!" said Margaret Ngaluma, an office worker in her 40s. "You could say we are the happiest people in world right now." Messages of congratulations on billboards and banners and walls across the city reflect that feeling. A multinational beer company offers "a toast to a new nation".

The Sudan People's Liberation Army (SPLA), which was the rebel force during the war, "vow[s] to protect our country". A small political party describes independence as the "most precious diamond extracted" during the struggle for freedom. The South Sudan Islamic Council banner says simply: "Oh God Bless South Sudan."

Given that virtually every family in the south of Sudan was affected by wars that have haunted the region for most of Sudan's post-independence history, the emotion and enthusiasm is unsurprising.

For young people, such as Eunice Aya, 22, whose education was stalled when she had to flee into the bush as a girl when conflict reached her village, independence brings hope of a second chance. "We'll have freedoms, to speak out, to have education," she said. "I can continue my schooling."

A rebel's story

For people of older generations such as Mamur, the feeling is more of pride and relief that their sacrifices and struggles have not been in vain.

"I was born in a war, grew up in a war, got old in a war," he said with a wry smile as he sat in his cousin's living room one recent evening.

That was just about true. He was born in Mundri, 116 miles from Juba, in 1953. Conflict erupted almost immediately, even before Sudan gained independence from Britain in 1956. Correctly foreseeing that the Arab-dominated north would seek to oppress, exploit and marginalise the south, where traditional beliefs and Christianity prevailed, southern rebels launched an uprising known as Anyanya I.

Mamur's initial schooling took place under a tree. It did not last long. When he was 10, he heard that his uncle, a teacher, had been arrested by northern forces, paraded in front of his fellow villagers, and then killed during a purge targeting educated southerners.

"Even at that age, something like that builds the anger in you," he said.

So Mamur joined the rebellion, armed with a basic hunting gun and a knife. So did his older brother, who was soon killed in battle. Mamur fought for six years before his father persuaded him to resume his studies in Juba. He had to start again at class one. Orders from the Khartoum government meant that instruction was in Arabic rather than English, a source of much discontent.

"I was 16 by this time – nearly a man!" Mamur said. "At school parade I had to kneel so I was the same height as the other pupils. Seriously!"

By the time he finished secondary school he was 28. It was 1981. The first civil war had been over for nearly a decade but another, even deadlier, conflict was brewing. Two years later, a group of southern soldiers, led by a US-educated colonel, John Garang, mutinied and began a new rebellion, Anyanya II, against the northern government, which had continued to exploit the south.

Mamur did not take up arms again, but he strongly supported the cause. Through the church where he had started working, he helped recruit young fighters for Garang's SPLA. It was dangerous, since Juba was a garrison town controlled by the northern forces, as locals here were reminded this week when dozens of old shells and mortar bombs buried by Khartoum's army were removed from the site of the independence celebrations.

After being detained three times by northern soldiers, Mamur escaped to Uganda with his wife in 1990, and then on to Kenya. But he could not stay away from his homeland. In 1994, with the war raging, he returned to southern Sudan to work for an international aid agency, all the while "operating undercover for the [rebel] movement".

A decade on, with the war nearly over, and about two million people dead, most from conflict-related starvation and disease, he returned to Kenya, where his wife and his two daughters were still living. It was there that Bashir and Garang signed the comprehensive peace agreement in January 2005, which provided for a six-year interim period of substantial autonomy for the south, followed by a vote on independence.

Mamur was part of a delegation that flew to Khartoum to attend Garang's inauguration as the country's first vice-president, but he still doubted that the south would ever be allowed to secede.

"We knew that the Arabs [the northern government] never kept their word on anything," he said.

But despite hitches – including Garang's mysterious death in a helicopter crash just months later – the peace deal held and the referendum inched closer. By 2009, Mamur came to the conclusion that independence may in fact happen. So he went to a men's shop in Nairobi and bought his freedom suit.

Last July, he returned to Juba for good, erecting a tent on a plot near his cousin's house as he waited to build a simple thatched hut. His suit came with him.

After staying up all night on Friday, he will put it on and make his way to Garang's mausoleum, where the independence ceremony will occur. When, around midday, the South Sudan flag is raised, he will go home.

A goat will be slaughtered, and a feast will ensue. Then he will take off his suit, its purpose served, and go to sleep a happy man.

"Even if I die on Sunday, it will be in a free country," he said. "I will die knowing that my people and children are free at last."