Sporting a red cap, red-and-white shirt and expensive designer watch, Uhuru Kenyatta gripped the microphone and whipped up thousands of supporters ahead of Monday's general election in Kenya.

Voters will go to the polls fearing a replay of 2007-08's post-election violence and aware that surveys show a 50/50 chance they are about to elect a president charged with crimes against humanity.

At Kenyatta's final rally in a downtown Nairobi park on Saturday, there was no clue that this is a man who ranks alongside Ugandan warlord Joseph Kony, Libya's Saif al-Islam Gaddafi and Sudanese president Omar al-Bashir in the eyes of the international criminal court (ICC).

Waiting patiently for six hours in unforgiving heat, fans scrambled for caps and T-shirts, hung off lamp-posts and trees and cheered wildly when Kenyatta's helicopter flew overhead. Finally, the deputy prime minister appeared and told the sea of red: "We've come a long way and been through a lot of ups and downs. One of the challenges we faced was people claiming we can't run because of the charges of the ICC. But God has opened a door for us and we were cleared by the [Kenyan] courts to run."

He said of Raila Odinga, his chief rivalry for the presidency: "He should accept that the will of the people is the will of God."

Kenyatta is among four Kenyans facing ICC charges for engineering ethnic violence that killed more than 1,100 people and uprooted 600,000 after the last election. Prosecutors accuse him of bankrolling the outlawed militia group Mungiki as it carried out revenge attacks.

Kenyatta's trial was due to begin next month, just when he is likely to face a run-off vote against Odinga if Monday's poll is tight, but ICC officials have indicated that it could be delayed until later this year.

One of Kenyatta's co-accused is his running mate, William Ruto. Their Jubilee coalition has united two of Kenya's biggest communities, the Kikuyu and Kalenjin, who were locked in deadly clashes last time.

Some predicted, or hoped, that the ICC charges would scuttle the "UhuRuto" ticket. In a live TV debate Odinga suggested his rival might one day have to govern by Skype from the Hague. In fact Kenyatta and Ruto appear to have gained sympathy from voters wanting to send a defiant message to "western imperialists" interfering in Kenyan affairs.

David Kamau, 63, a veteran of four violent elections, said: "It's wrong for anyone to come from outside, even if they are seeking truth. It's Kenyans who should judge which way it should go. In your own home, can anyone else come and determine your issues? All these decisions should be left to Kenyan citizens."

The Kenya Human Rights Commission opposed Kenyatta and Ruto being allowed to run with the charges hanging over them, but the country's courts decided otherwise. George Morara, senior programme officer at the commission, said: "They've been very ingenious at the turning the whole thing into 'the west versus Kenya'. It's terrible to have a country where poor people can be turned like marionettes."

Kenyatta, who is married with three children, has other cards to play: his youth – at 51 he would be Kenya's youngest leader – his name and his wealth. He is the son of the country's founding president. Jomo Kenyatta's face is ubiquitous on the national currency and the biggest international airport is named after him.Uhuru - a Swahili word for freedom - Kenyatta grew up in privilege unimaginable to most Kenyans. He attended one of the top schools in Nairobi before studying political science and economics at Amherst College in America. He inherited vast tracts of land and is ranked by Forbes magazine as the 23rd richest person in Africa with an estimated £330m. The family owns a TV channel, newspaper and various radio stations.

A well-resourced election campaign has included giant "UhuRuto" billboards showing the two men standing shoulder to shoulder, aggressive drives on Facebook and Twitter and an eight-page advert in one of the country's leading newspapers on Saturday.

Thousands of police officers will be on duty on Monday, with 14 million people expected to vote.

Victory for Kenyatta would put the world in uncharted diplomatic waters: it would be the first time a nation has democratically elected a politician indicted by the ICC. Given Kenya's status as a key western ally, not least in the fight against terrorism in neighbouring Somalia, a diplomatic headache looms.

Analysts at the International Crisis Group say that "regardless of the outcome of their cases, a president facing a lengthy trial before the ICC could potentially have extremely damaging implications for reform and foreign relations."There has been speculation in the Kenyan press that the country could be slapped with sanctions, imperilling the economy. Ngungi Githuku, a human rights activist, said: "If the election goes the way of those indicted by the ICC, is that the end of the ICC process? The culture of impunity will be stronger: as long as you have weight and money, anything goes. We will have sanctions on this country. Diplomatic quarters have made it clear that it won't be business as usual."

Britain's standard position on ICC indictees – to avoid all contact unless "essential" – and US assistant secretary of state Johnnie Carson's warning that Kenya's choice will have "consequences" have ruffled feathers here. But the EU has been at pains to avoid the word "sanctions" and officially pronounce that the Kenyan people must decide.

Kiama Kaara, programmes coordinator of the Kenya Debt Relief Network, said: "Kenya is too important to the international system for it to collapse. As long as it goes through the election and institutions, it becomes a hard sell to isolate Kenya on the basis of the outcome. If Uhuru Kenyatta wins free and fair, the international community would need to come up with a viable framework that does not punish the Kenyan people for their choices."

George Morara added: "The west will be reluctant to impose sanctions. They'd rather do business with Uhuru Kenyatta like they did with Mobutu [of Zaire] for 30 years. It will be for Kenyans to deal with it. I hope the internal tension doesn't mean that Kenyans turn on each other."

The ICC says the Rome statutes do not prevent Kenyatta and Ruto from running for election. Asked if she fears their election would embolden them to resist the court, Maria Mabinty Kamara, the ICC's outreach coordinator for Kenya and Uganda, said: "We'll cross that bridge when we come to it. So far they have fully participated and cooperated and there is no reason to believe that won't continue."