Kenya’s last presidential polls, in December 2007, led to disputes and violence that left nearly 1,500 people dead, and about half a million displaced.
Wednesday has been declared a public holiday to allow as many people as possible to vote.
“This was initially expected to be a low-risk exercise supposed to receive a unanimous endorsement,” says RFI’s Billie O’Kadameri in Nairobi.
“But it became controversial after key politicians teamed up with the churches to oppose the draft, raising fears some provincial areas whose leaders oppose the draft, could be trouble spots.”
But key supporters have been keen to calm fears ahead of the historic vote.
“[Kenyans] are united as we have never been since independence more than 45 years ago,” a senior advisor to Prime Minister Raila Odinga, Salim Lone, told RFI.
“Virtually all Kenyans, from across the political and ethnic divides, want this constitution.”
The draft constitution places checks on the president's power and makes the state's main institutions generally more democratic.
But the new text, one of the key items on the reforms agenda agreed upon in the aftermath of the election chaos, also creates a commission tasked with reviewing land policies.
The backbone of the "No" camp in the referendum campaign is the locally dominant Kalenjin tribe, whose leaders claim the new constitution would lead to taxation or even seizure of their land by the government, dominated by Kikuyus and Luos.
Public campaigns ended Monday but both sides continue to advertise in the media, hoping to swing the vote in their favour.