"All the credit" for the meeting went to the Kenyan political leaders, Tillerson said, in response to a question as to whether the USA had a role in organising it.
The truce comes months after Kenyans went to two violent elections in the last quarter of 2017.
Earlier this year, Mr Odinga swore himself in as the "people's president" and refused to recognise election victor Mr Kenyatta as head of state.
Bilowgii sanadkan, Mr. Odinga ayaa isu dhaariyey Madaxweynaha shacabka waxa uuna diiday in uu Mr. Kenyatta u aqoonsado in uu doorashada ku guuleystay oo uu Madaxwayne yahay.
President Uhuru Kenyatta with US Secretary of State Rex Tillerson.
The US diplomat, who arrived in Nairobi on Friday, had been due to visit the AIDS-relief programme PEPFAR on Saturday and also attend a ceremony marking 20 years since Al-Qaeda bombed the US embassies in Kenya and Tanzania, killing 224 people.
"As Raila Odinga and Uhuru Kenyatta toast, hug and laugh in Nairobi, I remain marooned in Canada because I swore the former in at Uhuru Park on January", he says.
At Tillerson's two news conferences on Friday, in Djibouti and Nairobi, the typical arrangement for news conferences involving the secretary and his counterpart in the host country were changed, American reporters travelling with Tillerson said.
He called Odinga "his brother" on Friday and promised "we will begin a process of bringing our people together" after the elections.
In a statement posted in his Facebook page and on his official Twitter handle, Mr Miguna said Mr Odinga's "erratic decision to betray the fight for electoral justice" can not be justified.
He said they have agreed to stop any dissent immediately and not to allow the country's diversity to kill their nation.
Koigi was also in and out of the dark rooms under both Presidents Jomo Kenyatta and Daniel Moi, in the 80's, as a result of his "rebellious and troublesome" nature.
"The US should not be dismissed or discounted".
Meanwhile, Thirdway Alliance Party Leader Ekuru Aukot said the move by the two leaders will help guide the national conversation on issues affecting Kenyans.
"It's a really good step towards harmonizing the country", said Brian Wanjoki, a pedestrian.
That's not a coincidence, said independent political analyst Martin Andati.
Waxaa ku guuleystay doorashadii ku celiska ahayd ee Kenya ka dhacday bishii October ee sanadkii 2017 Uhuru Kenyatta, taasi oo Mr. Odinga uu qaadacay.