High-ranking government officials saw off Mr Ruto at the airport in Nairobi.
Mr Ruto and President Uhuru Kenyatta have been charged with crimes against humanity, which they deny.
On Sunday, Mr Kenyatta said the ICC must stagger their trials as the constitution did not allow the two men to be out of Kenya at the same time.
Mr Kenyatta is due to go on trial in November.
Political ploy?
Radio boss Joshua arap Sang has also been charged with inciting and helping coordinate attacks.
He will be tried alongside Mr Ruto, and is already at The Hague, AFP news agency reports.
He too denies the charges.
The charges against the three stem from violence that broke out after disputed elections in 2007, in which more than 1,000 people were killed and 600,000 forced from their homes.
Mr Kenyatta and Mr Ruto were on opposite sides during the 2007 election and are accused of orchestrating attacks on members of each other’s ethnic groups but formed an alliance for elections in March this year.
Analysts say the ICC prosecutions bolstered their campaign as they portrayed it as foreign interference in Kenya’s domestic affairs.
On Saturday, Mr Kenyatta said all camps still accommodating families displaced by the violence would be closed by 20 September, the local Daily Nation newspaper reports.
He issued cheques worth more than $4,500 (£3,000) per family so they could move out of camps and rebuild their lives.
He and Mr Ruto closed some camps in Eldoret and Nakuru in Rift Valley province, which was badly affected by the violence.
The timing of the government hand-outs and closure of the camps will raise suspicion that it is a political ploy ahead of Mr Ruto’s trial, says the BBC’s Caroline Karobia in the capital Nairobi.
However, it should be remembered that Mr Kenyatta and Mr Ruto only took office in April and had pledged to help survivors of the violence, she says.
More than 40,000 people are estimated to be still living in the camps.
The two leaders prayed together at a church on Sunday.
“We will work with [the] ICC, and we have always promised to do this,” Mr Kenyatta told a rally of supporters.
“But it must understand that Kenya has a constitution, and Ruto and myself won’t be away at the same time.”
The president said the charges were “false and will be dismissed”.
“The plotters of this scheme will be named and shamed. The victory won’t be Ruto’s, Sang’s or mine, but for Kenya,” he said to cheering crowds.
As government ministers and MPs saw him off at the Jomo Kenyatta Airport in Nairobi on Monday, Mr Ruto said: “Gentlemen, take care of this great nation,” the local Daily Nation newspaper reports.
On Thursday, Kenya’s parliament passed a motion calling for Kenya to withdraw from the ICC.
The court said the cases would continue, even if Kenya withdrew.
In May, the African Union accused the ICC of “hunting” Africans because of their race.
The ICC strongly denies this, saying it is fighting for the rights of the African victims of atrocities.
The ICC was set up in 2002 to deal with genocide, crimes against humanity, war crimes and the crime of aggression.
The court has been ratified by 122 countries, including 34 in Africa.