Sonko, a presidential candidate and President Macky Sall's fiercest critic, has faced a string of legal woes, which he claims have been designed to keep him out of politics.
His sentencing in absentia to two years in prison last month in a moral corruption case sparked clashes that left 16 dead according to the government, 24 according to Amnesty International, and 30 according to Sonko's PASTEF party.
But he had not been jailed despite that sentencing.
On Friday he was arrested on new allegations tied to comments he has made, rallies he has held, and other episodes since 2021.
The new charges include undermining state security, criminal association with a terrorist body, disseminating false news and theft.
"I have just been unjustly placed in custody", Sonko wrote on Facebook on Monday afternoon.
"If the Senegalese people, for whom I have always fought, abdicate and decide to leave me in the hands of Macky Sall's regime, I will submit, as always, to divine will", he said.
Less than two hours after Sonko's indictment, the interior minister announced that PASTEF would be dissolved for having "frequently" called for insurrection, leading to destruction and the loss of life.
Senegal's public prosecutor said Saturday that this new legal affair had "nothing to do" with the high-profile moral corruption case for which Sonko was sentenced on June 1.
That verdict makes him ineligible to context next year's presidential election.
But his lawyers have argued that his arrest on Friday cancelled out his conviction in the moral corruption case, because he had been tried in absentia.
"It's a farce," Cire Cledor Ly, another of Sonko's lawyers, told reporters outside the courthouse on Monday.
"It's a plot that was formed, thought out, planned and executed."
Sonko on Monday continued a hunger strike he began a day earlier, his lawyers said.
They said there was no limit to his detention time as the new charges are criminal.
"The judge can retain him until the case is heard", Babacar Ndiaye, one of the lawyers, said.
Sonko was arrested on Friday after claiming on social media that security forces had been filming him outside his house and that he had snatched one of the phones to ask them to delete it.