The passage of the Democrat-sponsored charter amendment proposal which would bring back the two-ballot system is a win for all major political parties, including the ruling Palang Pracharath Party whose draft was rejected by the Senate.
The Democrat's draft legislation, which would raise the number of constituency MPs from 350 to 400 and restore the old selection formula for 100 list MPs, was the only one out of 13 bills that met the criteria for Senate support, obtaining 210 votes in favour from senators, in addition to 342 votes from House members.
To pass the first reading, charter change bills need a majority (at least 367 votes) of the combined membership of the House of Representatives and the Senate, with support from at least one-third of the senators, or 84 votes.
The senators either abstained or voted down the PPRP's bill, which targeted Sections 144 and 185 of the charter seen as its core protection against corruption.
Stithorn Thananithichote, director of the Office of Innovation for Democracy at King Prajadhipok's Institute, said: "The Senate's rejection of the PPRP's charter proposal was a big boost for Gen Prayut who had voiced disagreement with the changes."
On Wednesday, when parliament began its two-day joint sitting of MPs and senators to consider the 13 charter amendment bills tabled by political parties, government spokesman Anucha Burapachaisri said Gen Prayut wanted the two sections kept intact as they were effective in warding off graft.
However, Mr Stithorn said even though the party's draft was shot down, the PPRP still stood to benefit from the passage of the Democrat Party's version.
He also pointed out that Gen Prayut and the PPPR had not lost face from this either as the PPRP's draft was largely attributed to Paiboon Nititawan, a PPRP list-MP.
The Pheu Thai Party's draft, which also targeted the election system, did not get enough support because it included "switching off" the Senate, he said.
Democrat leader Jurin Laksanawisit on Friday thanked the MPs and senators for their support on Facebook, saying the draft's passage was "the light at the end of the tunnel" and would lead to amendments of other key issues.
Jade Donavanik, a legal scholar and former adviser to the Constitution Drafting Committee, said he believed the Democrat Party would push for further changes during the scrutiny process.
It was likely that the coalition partner would go for the mixed-member proportional system, similar to the one adopted by Germany, he said.
Under the system, if a party's popular vote accounts for 10% of ballots cast, then it will receive 50 of the 500 House seats. If the election had only seen it earn 40 seats from the constituency system, it would therefore be allocated 10 party-list seats to make up the deficit.
Mr Paiboon, who had initiated the PPRP draft, could not hide his frustration after the Senate rejected the PPRP's vision for the charter.
"We talked to them and most agreed with the proposal. Several also accused the party of trying to abuse the budget, so I think there is no need for me to be protective of the Senate," he said.
Parliament has set up a committee consisting of 30 House members and 15 senators to scrutinise the bill within 15 days.
The committee scheduled its first meeting for next Tuesday.