His body lay in state early Friday, for a third straight day, for a final viewing before being placed in a black limousine for the short drive to the funeral site under military guard.
Among those who viewed Mills’ body before the service were Ivory Coast’s President Alassane Ouattara, Ellen Johnson Sirleaf of Liberia as well as the leaders of Benin and neighbouring Togo.
US Secretary of State Hillary Clinton was due to attend the funeral.
“He was like a brother to me. I will surely miss him,” Togolese President Faure Gnassingbe told journalists.
Benin’s leader, also the current African Union chairman, Thomas Boni Yayi, described Mills as “passionate about peace in Africa and in the region.”
His death on July 24 following an illness came as a shock to many Ghanaians, despite rumours that he had been sick and reports that he suffered from throat cancer.
Mills’s death just five months ahead of polls in which he was to seek re-election upended the presidential race in a country that recently became a significant oil producer and is praised as a stable democracy in an often turbulent region.
Organisers said roughly 10,000 people were expected to attend the 90 minute ceremony, after which Mills’s body will be taken to Osu Castle, the official presidential residence, for burial.
A special seating area had been set up for the 16 heads of state and other dignitaries who are due to attend.
Clinton, currently on an African tour, arrived in Accra late Thursday after a brief stop in Nigeria’s capital, where she met with President Goodluck Jonathan.
For those unable to access the grounds, funeral organisers have set up large television screens that will broadcast the ceremony, visible to people on the square’s periphery. The event will also be shown on national television.
Some, however, arrived early and secured a place in the square, which was filling up rapidly.
“Today is my saddest day,” said Akua Danso, an 80-year-old former teacher who was confined to a wheelchair, being pushed by her grandson.
“I have seen presidents come and go but he was the best. He was very humble. I wish I had the opportunity to meet him while he was alive, just to tell him that he was a gem,” she told AFP.
For a brief period, a helicopter hovering over the area dropped flyers that urged peace in Ghana’s December vote.
“We want peaceful elections in 2012,” read the flyer.
Mills former vice president John Dramani Mahama was sworn in to serve out the remainder of Mills’s term hours after his death, as dictated by the constitution.
The new president is expected to be endorsed by the ruling party to run in the December election, which analysts say is likely to be close.
Ghana, a country of some 25 million people, has begun producing oil from its offshore Jubilee field, one of the largest discoveries in West Africa in recent years. The field’s operator Tullow has estimated that the field’s recoverable resources amount to up to one billion barrels.