Democrat Party leader Abhisit Vejjajiva told a news conference it would not be fielding candidates, saying: “Thai politics is at a failed stage.”
PM Yingluck Shinawatra called the election earlier this month in a bid to end weeks of mass protests.
The head of the Thai army has warned the country’s political divisions could “trigger a civil war”.
General Prayuth Chan-ocha has proposed a “people’s assembly” – made up of civilians from both sides, not the leaders, to heal the divisions.
The opposition-backed protests in Bangkok have caused Thailand’s most serious political turmoil since 2010.
Yingluck Shinawatra won the last elections in 2011, but protesters say her brother – the controversial ousted former leader Thaksin Shinawatra – remains in charge.
At his news conference, Abhisit Vejjajiva told reporters his party had agreed it would not field candidates in the snap elections.
“The Thai people have lost their faith in the democratic system,” he said.
The prime minister dissolved parliament and called the election on December 9 in a bid, she said, to avoid violence on the streets and “to give back the power to the Thai people”.
Her Pheu Thai party has a majority in parliament, and draws significant support from Thailand’s rural areas. It is seen as well-placed to win February’s election.
General Prayuth Chan-ocha said he was deeply concerned by the latest crisis, with divisions not just in Bangkok but across the whole country.
“The situation could trigger a civil war,” he told the Bangkok Post.
Setting out his vision of a “people’s assembly”, he said it should be made up of people from both sides of the political divide – known as the “red shirts”, those who support Thaksin Shinawatra, and the “yellow shirts”, those who oppose him.
“It must be from a neutral group and comprise non-core representatives of all colors, and all color leaders must be excluded,” he said.
General Prayuth Chan-ocha did not give details on how or when the assembly would be set up, but said any proposal “must come from a public consensus and the public must brainstorm how to reach that consensus”.
He stressed his grouping would be different to the “people’s council” proposed by the opposition.
“The people’s assembly must not be organized or sponsored by any conflicting group, as it would not be accepted by the other side,” he said.
His comments came after a defense council meeting on Friday to discuss the February 2 election.
Defense spokesman Col Thanatip Sawangsaeng said the army “is ready to support the Election Commission in organizing the elections when asked”.
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