The ruling relates to Samak Sundaravej's appearance in a TV cooking show.
Thailand's constitution bans the premier from working for private companies. The prime minister earlier admitted that he had been paid for his appearances on the Tasting and Complaining show, but said it was a freelance job.
The ruling removed Samak Sundaravej from office immediately, but other ministers will continue to perform their duties as caretaker ministers until a new government is formed. Current First Deputy Prime Minister Somchai Wongsawat will assume the duties of prime minister.
"His term is over, and the term of the Cabinet has also expired, although according to the constitution they [the Cabinet ministers] must remain as an acting government until a new administration is installed," the newspaper quoted Constitution Court judge, Chat Chawakorn, as saying.
Sakchai Khaewwaneesakul, the managing director of the company that produced the TV show, said the company paid the premier 80,000 baht ($2,300) for the four shows.
The initial complaint was filed by a group of opposition senators from the People's Alliance for Democracy party and came amid nationwide anti-government protests and the introduction of martial law last week after a protester was killed. Anti-government protesters took over the grounds of Government House on August 26 and have refused to move despite the imposition of a state of emergency.
