The protest signals the frustration felt by many across Kuwait that the country has remained stagnant as its neighbours, such as Qatar and the United Arab Emirates that is home to Abu Dhabi and Dubai, grow and flourish.
Kuwaitis at the protest said they are frustrated that despite their country's oil wealth, much is being siphoned off the top by corrupt officials.
Despite the protest taking place after sunset, temperatures soared in Kuwait City.
Kuwait prides itself on having the Gulf's most free-wheeling political system and a vibrant press, but denouncing the Western-backed emir is illegal.
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The emir, Sheik Sabah Al Ahmed Al Sabah, was chosen by the ruling family in 2006 after an internal power struggle that followed his predecessor's death.
Kuwait's top court earlier this week overturned an appeals court acquittal and sentenced three other former opposition lawmakers to 20 months in prison for insulting the Western-backed country's ruler, though they will be allowed to remain free on bail.
"It's such a refreshing sight to see all of these faces here today. All of these people have come to deliver a message: All these people here are here to save Kuwait from corruption, to say they've had enough," former lawmaker Jamaan Al-Hirbish told the crowd from atop a stage.
The protest today was being led by former opposition lawmaker Musallam al-Barrack, whose group has promised to launch a series of street protests to press for reform in the Gulf state.
The group is calling for allowing citizens to run for the prime minister's post. Kuwaiti prime ministers are currently appointed by the emir and are from the ruling family.