
"The Democrats are ready to contest early elections, which can happen at any time from now," he said.
Some 4,000 party supporters are expected to attend the dinner and contribute to campaign funds at the Impact Muang Thong Thani convention centre.
Suthep said he expected to see a House dissolution soon due to the political polarisation.
As a token of appreciation for support, the Democrats plan to distribute several souvenirs, such as a book "Confidence in Thailand, Trust in the Democrats" written by party leader Abhisit Vejjajiva, he said.
Aside from dinner entertainment provided by the Bangkok Symphony Orchestra, Abhisit will make a speech offering his views on how to overcome the political turmoil, he added.
He said he did not anticipate disruption to the dinner. Last month, pro-government crowds dressed in red rallied at a Democrat function in Chiang Mai, causing its cancellation.
The Democrats are prepared to contest the elections again and again until they can achieve victory over former prime minister Thaksin Shinawatra, Suthep said.
"I truly believe no one can forever fool 63 million Thai citizens," he said, claiming the Democrats are genuine believers in democratic principles while Thaksin is an imposter.
He said his party would carry on fighting to win the trust to govern the country.
He did not expect any impact on the elections if coalition parties, including People Power, were penalised by being disbanded. The dissolved parties can be reborn under a new banner, he said.