The decision was taken just hours after their newly proclaimed leader urged them to end their boycott.
"The decision has been taken...The New Forces will return to the government," said Sidiki Konate, a spokesman for the rebels.
The rebels had withdrawn from the government in September in protest against the slow pace of peace talks.
Major Ibrahim Coulibaly, declared leader of the The New Forces on Friday, also called on President Laurent Gbagbo to put aside political differences and adhere to the stalled peace deal both sides worked out in France in January.
He made the call as rebel and government troops withdrew heavy arms from a front line policed by French and West African peacekeepers that splits the world's top cocoa grower into the rebel-held north and government-controlled south.
"I have just ordered each of our ministers to return to their posts on Monday, 22 December, and to work resolutely and devotedly for the rigorous application of the Marcoussis accords," Coulibaly said in a statement issued in Paris.
The government and rebel forces agreed last January in Marcoussis, near Paris, to form a power-sharing government in which rebel representatives had nine seats.
"I also invite President Laurent Gbagbo to work resolutely as well... to put the country's higher interests over political calculations and suspicions and deliver a speech about
the official end of the war," he said.
"We think today that the empty-chair policy was a bad thing"
spokesman for Coulibaly
Coulibaly - who called himself a major, although supporters in the rebel stronghold of Bouake described him as a sergeant - was among a group of suspected mercenaries detained in Paris in August on suspicion of plotting to kill Gbagbo.
The rebels pulled out of the government in September, accusing Gbagbo of stalling the peace process and not consulting them over the naming of the defence and interior ministers, appointed almost six months after the government was formed.
Muhammad Diakite, a spokesman for Coulibaly, confirmed that the rebels had changed their position. "We think today that the empty-chair policy was a bad thing," he said.
Ivory Coast tumbled into civil war in September 2002 after a failed coup by disgruntled soldiers seeking to oust Gbagbo. Thousands of people were killed and more than a million forced from their homes in the violence.