In a 6 to 3 vote, the court ruled that the election violated the constitution, as voting had not taken place in 28 districts in southern Thailand where candidates were unable to register due to blockades by the anti-government protesters.
"The Feb. 2 election could not take place across the kingdom on the same day," the court said in a statement.
It was unclear when a new election would take place. Somchai Srisutthiyakorn, an Election Commission member, said the country had two options to organize a new vote.
"The commission could discuss with the government about issuing a new royal decree for a new date or we could ask the heads of all political parties to decide together when best to set the new election date," he told reporters.
If a new election is organized, the protesters say they will disrupt it again.
"If the court rules the election void, don't even dream that there will be another election. If a new election date is declared, then we'll take care of every province and the election won't be successful again," protest leader Suthep Thaugsuban told supporters late on Thursday.
The protests are the latest chapter in an eight-year crisis that pits Bangkok's middle class and royalist establishment against supporters of Prime Minister Yingluck Shinawatra and her brother, ex-premier Thaksin Shinawatra, who was toppled by the army in 2006 and lives in exile to avoid a jail term for graft.
Now in their fifth month, the protesters have shut government offices and at times blocked major thoroughfares in Bangkok to try to force Yingluck out. Twenty-three people have died and hundreds have been injured in the violence. REUTERS