Zimbabwean opposition lawmaker Job Sikhala was remanded in custody on Thursday when he appeared in court on charges of trying to subvert the government.
The Zimbabwe Lawyers for Human Rights legal group said Mr Sikhala, vice-chairman of the Movement for Democratic Change (MDC) party, was remanded in custody until July 24.
"He appeared before a magistrate and was charged with attempting to overthrow the government unconstitutionally," Kumbirai Mafunda, spokesman for the lawyers' group, told AFP.
Mr Sikhala, an often outspoken senior official in the MDC party, allegedly said in a speech at a weekend rally that the party would unseat President Emmerson Mnangagwa before the next election.
"We are going to overthrow him (Mnangagwa) before 2023," he was quoted as saying.
Mr Mafunda said Mr Sikhala's lawyers were preparing a court application for his release on bail, and that they had complained about his treatment by police and being denied access to legal advice.
Mr Sikhala had been expected in court in Harare on Wednesday but was driven to the southwestern rural town of Bikita to appear before magistrates.
Some Zimbabweans hoped that the ousting of long-time autocrat Robert Mugabe in 2017 would usher in a more tolerant political scene as Mr Mnangagwa sought to attract foreign investment.
But government critics have been frequently targeted by the police and security forces, while the country's economy has lurched into a new crisis of rocketing inflation.
The ZANU-PF government reacted furiously to Mr Sikhala's alleged remarks, with information secretary Nick Mangwana describing the speech as an "insurgent rant".
Mr Mnangagwa promised a fresh start for Zimbabwe after decades of repression and economic decline under Mr Mugabe.
At least 21 people have been arrested and charged with treason since January.