Sub Lt Samdin Lertbut, a representative of the Kong Thap Tham (Dhamma Army), affirmed the group's participation during a press briefing at the club yesterday.
The Dhamma Army has close ties with PAD core leader Chamrong Srimuang - a prominent figure in the protests leading to the 2006 coup that overthrew the Thaksin government.
The group will play a supporting role in tomorrow's rally, and will be involved in the management of food, medical supplies, sanitation and shelter.
The group previously called for the resignation of the governments of Thaksin Shinawatra, as well as those of Samak Sundaravej and Somchai Wongsawat, whom the yellow shirts accused of being proxies for Thaksin.
Sub Lt Samdin said the Dhamma Army was happy and willing to support tomorrow's gathering of the Pitak Siam (Protecting Siam) group. The rally is being organised by Gen Boonlert Kaewprasit, president of Class 1 of the Armed Forces Academies Preparatory School (AFAPS) and a classmate of former prime minister Gen Surayud Chulanont.
The rally is being held with the aim of purging "disgraceful" politicians from government, Sub Lt Samdin said, adding that it would be peaceful.
Gen Boonlert said the Pitak Siam rally has not received backing from any political groups. He said the gathering will simply be a stage where participants will be able to listen to facts.
He said he hoped those who join will be able to spread the message to those who cannot attend. Gen Boonlert said an assessment would be made of the success of tomorrow's rally, and that would influence any decision to hold a repeat event.
He also said the second phase of the movement would be to oust the government, saying it would be completed within a day if it went ahead.
He also played down the likelihood of violence, despite a red-shirt demonstration being held close to the rally site. He said anyone attempting to incite violence will be recorded by the media, and perpetrators will be held to account.
He said the rally is aimed at stopping the government's three main failings - allowing the monarchy to be insulted; being a puppet of ousted prime minister Thaksin; and corruption.
Thai citizens based in the US will also set up a stage there and hold a demonstration concurrently with the Pitak Siam rally, he added.
Guest speakers on tomorrow's Bangkok stage will include: Surapong Chainam, former Thai ambassador; Gen Pathompong Kesornsuk, former chief adviser to the Supreme Command; Seri Wongmontha, a prominent political critic; and Sqn Ldr Prasong Soonsiri, former secretary-general of the National Security Council.
All of the speakers are mainstays of the yellow-shirt scene.
Sqn Ldr Prasong, who took part in yesterday's media briefing, said the time had come for Thailand to rid itself of the corrupt and intransigent politicians who are running the country.
He said the second round of the movement will follow shortly after tomorrow's rally, and that it would achieve a definitive resolution to the group's demands.
Sqn Ldr Prasong said this week's cabinet reshuffle had been carried out to serve the government's interests, not for the benefit of the public.
He said if the government's policies of self-interest remained the same, then it was unlikely their demands could be met.