Palace officials said the body would be placed in a coffin with a symbolic royal urn near it.
Soldiers in ceremonial dress have been gathering outside the palace, where the grass appears to have been freshly laid overnight.
The procession was expected to be led by a senior monk, Somdej Phrawannarat, who also led the prayers during the 2008 funeral of the king's elder sister, Princess Galyani Vadhana.
The Crown Prince Maha Vajiralongkorn, who has been named as successor, will also be at the procession.
The royal family travelled to the Grand Palace by motorcade.
On Friday evening, Prince Maha Vajiralongkorn will conduct the bathing ceremony for his father's body - a traditional Thai Buddhist funeral rite.