Azimio la Umoja leader Raila Odinga is the first person to sign the signature collection roll, aimed at ousting President William Ruto.
The Opposition had last week announced that he would launch the signature collection drive on Friday.
"The people have started the process of taking back the power given to people to represent them. We have to know how many we are and that is why we have started collecting signatures," he said.
The drive is aimed at collecting 10 million signatures to show dissatisfaction with the leadership of President William Ruto and his deputy Rigathi Gachagua.
"I Raila Amollo Odinga will start here today. You will also get the papers to sign so that by next week we have 10 million."
The Opposition has been protesting over the high cost of living and high taxes imposed on Kenyans by the recently passed finance bill.
Raila said the people have the power to choose who can represent them.
He said the person who rigged himself into power has gone against his promises and that the people have taken it upon themselves to reclaim their authority.
Last week, Azimio said they had resolved to embark on a campaign of defiance and civil disobedience which will take different forms at different times.
DAP - K leader Eugene Wamalwa said the defiance would include refusal to pay taxes whose aim is to push President William Ruto out of office.
As a result, he said, Azimio would on July 7 unveil nationwide civil disobedience.
'There will be a mass signature collection to signal the withdrawal of sovereignty from officials in the government who supported the Finance Bill," he added.
