The defamation suit was filed at the Milimani Law courts and will be placed before the civil division court for directions Thursday.
Sonko had initially given Kidero seven days to apologise over statements he made at a public gathering last month where he allegedly accused him of being a drug dealer.
In his suit papers, Sonko accuses the governor of engaging in a smear campaign against him by issuing defamatory statements, which are considered to be scandalous and malicious.
READ: Sonko gives Kidero 7 days to apologise
The senator through his lawyer Danson Mungatana, says his charitable organisation has started incurring huge loses as some of contracts for provision of services to the poor have been cancelled.
Mungatana will be seeking a court injunction barring Kidero from making similar statements.
Kidero without mentioning names had sensationally claimed that Nairobi was the centre of drug trafficking adding that certain people had been named as having been involved in drug trafficking but no action had been taken against them.
“Where drug cartels fight, they tend to get into positions of authority. This happened in Jamaica, Cuba and even in Colombia. Any services given must be given within the confines and provisions of the law,” said Kidero.
The governor appeared to cleverly hit out at the Senator who operates a rescue service dubbed ‘Sonko rescue team’ consisting of ambulances and hearses saying he was using the vehicles to transport and supply the drugs to city dwellers.
Sonko claims Kidero has through this disparaged his reputation and caused him to be shunned by friends.
Governor Kidero is said to have uttered the defamatory statements while addressing a public gathering in Mathare area Nairobi County on June 22.
The article was published in the Star newspaper under the headline “Kidero says Sonko is a drug peddler”.