The Maldives government accused Sheik Imran, leader of Islamic conservative Adhaalath or Justice Party of inciting violence among the protesters with the aim of overthrowing the government.
Imran had been a key organiser of the protest by three opposition parties and his arrest could exacerbate an acrimonious political climate in the Indian Ocean archipelago state.
Thousands marched in the capital accusing Gayoom of jailing former President Mohamed Nasheed and others who he sees as political threats.
Police fired tear gas and arrested 193 protesters. They later declared the demonstration was not peaceful, saying they will breakup any gathering without warning.
Maldives police told reporters that Imran "incited violence amongst protesters with the aim of toppling the government and called for clashes with the police if necessary."
However, Nasheed's Maldivian Democratic Party said the police charged the protesters without provocation.
The protesters also beat up two policemen who were flown to neighbouring Sri Lanka for treatment.
Nasheed's imprisonment after a rushed trial sparked widespread international condemnation.
In a statement after a fact-finding mission to the Maldives, the United Nations human rights office said Nasheed's trial was "vastly unfair and his conviction was arbitrary and disproportionate."
The statement, which noted that the delegation met with Nasheed in addition to government officials and members of civil society, also said the country's legal system is "perceived as politicised, inadequate and subject to external influence."
