After the last election, Odinga disputed results that declared the winner to have been the incumbent president, Mwai Kibaki. Odinga alleged the election had been rigged.
Protesters took to the streets, where supporters of both camps fought one another. More than 1,200 people were killed and hundreds of thousands displaced -- the worst violence since the nation gained independence.
Optimistic, but prepared
Leading up to this election, the candidates declared they would settle any election disputes in court.
Candidates have implored their supporters to avoid bloodshed, no matter the vote's outcome.
But some citizens remained wary.
"I don't know what possessed people last time," Kamau said of the violence. "I hope there will be no violence. I'm waiting for Kenya to restore my faith this time."
But as he waits, he is prepared. His refrigerator is stocked and his car is filled with fuel.
"Just in case," he said. "You never know."
'My main issue'
The economy, security and the fight against corruption, which is rampant in the country, are among voters' top concerns in the election.
The election also poses a challenge: Kenyatta has been indicted by the International Criminal Court for allegedly inciting a local militia to conduct reprisal attacks in the last election. He has denied the charges.
His running mate, William Ruto, also faces ICC charges.
Though Kenyatta nevertheless enjoys widespread popularity, some voters expressed fear that the international community will isolate the nation if a candidate facing ICC charges is elected.
Dominic Muia, 35, was in line at 5 a.m. to cast his ballot in the town of Nakuru.
"My main issue is the economy," he said. "I'm voting for Uhuru (Kenyatta) because he is younger and has a better vision to move the country forward."
At 51, Kenyatta would be the youngest Kenyan president ever. Odinga is 68.
'Things an average citizen worries about'
Harrison Mario, 37, said his vote is based on issues and policies, and will go to Odinga.
"Basically, he has been fighting inequality." he said. "He has been campaigning for the less fortunate. His manifesto focuses on security, education and food -- things an average citizen worries about."
Both leaders are campaigning on almost the same policies, leaving the more than 14 million registered voters to choose based on criteria that include personality, ethnicity and links to political parties.
"I don't know that much about their differences, so I'm voting for the candidate of my favorite political party," said Susan Kamau, who lives in Nairobi. "In short, I'm voting on loyalty to my party, not issues."
In addition to the presidential race, the nation will also pick governors, senators and a slew of other local candidates under the new constitution.
Whoever wins, the race evokes memories of a political dynasty.