Yingluck flew out to Japan on Sunday with her son Supasek Amornchat. She is expected to spend at least five days away before returning. She plans to take her son and his friends to Disneyland while there, a source said.
Thaksin will meet Yingluck in Japan and both will fly in his private plane to India to carry out a merit-making ceremony from Friday to Sunday before returning to Thailand.
A number of former Pheu Thai MPs are expected to join the merit-making ceremony in India, the same source said.
Meanwhile National Council for Peace and Order spokesman Winthai Suvari said the NCPO had granted Yingluck permission to leave the country as she had followed the NCPO's demand to inform the council of her movements after her government was ousted on May 22.
Yingluck travelled to Europe and the United States from July 24 to August 11 after being allowed by the junta to leave on a temporary basis.
During the previous trip, Yingluck reportedly detoured from her declared destinations - she was seen in a photo with Thaksin and brother-in-law Somchai Wongsawat at a restaurant in Singapore, which she did not declare as one of the destinations in her schedule.