Wichian Chaowalit on Monday quit as a Palang Pracharath Party (PPRP) list-MP amid reports he would join the Sang Anakhot Thai Party co-founded by former PPRP leader Uttama Savanayana.
He tendered his resignation to the Office of the House's Secretariat on Monday.
Mr Wichian said it had been an honour to serve as an MP over the last three years with the PPRP, during which time he sat as a member of the House committee on the budget bill.
He did not give a specific reason for quitting, but said there were several things he wanted to do to serve the public.
"I'm considering where to pursue my work next and make a further contribution to the country," he told members of the press.
Mr Wichian was a co-founder of the PPRP and known to have connections with politicians close to former deputy prime minister Somkid Jatusripitak.
He was tipped to join the Sang Anakhot Thai Party which is holding a general assembly tomorrow.
Mr Wichian said he had informed the PPRP during the party's assembly on April 3 in Nakhon Ratchasima that he did not want to sit on the party's executive. However, he did say that he would quit.
Some also believe that three other MPs, Pornchai Trakulwaranont, Suraporn Danaitangtrakul and Chuan Chuchan will quit the PPRP and join Sang Anakhot Thai ahead of the next election.
Mr Suraporn and Mr Chuan were named list-MPs several months ago when Supol Fongngam and Santi Kirannant quit and moved to the Sang Anakhot Thai Party.
Pakin Sommitthanakul will replace Mr Wichian as a list-MP.
Meanwhile, Mr Uttama is tipped to be named Sang Anakhot Thai leader and Sontirat Sontijirawong as its secretary-general during the party's assembly tomorrow.
