The separatist Free Aceh Movement (GAM) and the Indonesian government signed a pact in Helsinki on August 15, 2005, aimed at ending a 30-year war in which 15,000 people died and giving the Acehnese greater power over their own affairs.
People from across the province, many from GAM stronghold areas, have arrived in Banda Aceh in the past two days.
Organisers expect more than 100,000 to take part in the rally.
The official anniversary celebrations on Tuesday will be attended by Martti Ahtisaari, a former Finnish president and the main mediator of the Helsinki talks; and Jusuf Kalla, the Indonesian vice-president, the architect of Aceh's post-tsunami peace process.
Last month, Indonesia's parliament passed a bill that paved the way for direct elections of executives in the Aceh province on Sumatra island's northern tip.
GAM officials welcomed the law but have said that some of its provisions must be amended because they are not in line with the peace agreement.
"We do not want to be fooled again"
Banner at the Aceh rally
One demonstrator, Rasyidin, a lorry driver, had little idea of the truce's content, although a banner on his truck said: "We do not want to be fooled again."
Others gathering around the provincial capital's main mosque at the start of the protest had clearer opinions.
Ibrahim Nyak Mad, a handicraft maker, said: "The Aceh people have the right to object if they have a problem with an iota in the bill. We are thankful for the truce, but we want to ensure it will not fail us.
"We are victims of the conflict. We are entitled to enjoy the entire deal," he said, insisting the rally was no GAM event.
Jakarta argues the bill has made Aceh the envy of other provinces. Sofyan Djalil, the information minister, said last week that giving Aceh additional powers could trigger lawsuits from those who think the province already has a good deal.
But Djalil, born in Aceh, has also said that amendments were possible "two years down the road" after implementation.
The main Baiturrahman mosque
was the gathering point
The international mission monitoring implementation has said the laws are broadly in line with the pact.
Pieter Feith, head of the Aceh Monitoring Mission, said in a statement his group would extend its stay beyond a September 15 deadline until December elections, although with a reduced force of 35 monitors.
Last year's deal, which followed months of talks between GAM and Jakarta, was spurred by the December 26, 2004, Indian Ocean tsunami that left about 170,000 people killed or missing in Aceh.