Prayuth Siripanich, a member of the Puea Thai Party, said ten lawmakers flew to Hong Kong on February 17 and returned on February 19.
Thaksin asked lawmakers to be united and not to break that unity, Prayuth said, adding that the ex-PM also requested the legislators meet their constituents because the election is fast approaching.
Thaksin served as prime minister from 2001 to 2006 when he was overthrown in a military coup supported by the Bangkok-based establishment.
His younger sister, Yingluck Shinawatra, was elected prime minister in 2011. She was overthrown in a 2014 military coup.
Yingluck fled Thailand last August, weeks before the Supreme Court found her guilty of negligence in mismanaging a rice subsidy scheme and sentenced her to five years in prison.
The siblings have been in Asia since early February, said party members, and have visited China, Japan and Hong Kong before travelling to Singapore on February 19.-VNA