Thailand has completed the election process of the House of Representatives after the last three MPs out of the total 500 were verified on Tuesday.

Sawaeng Boonmee, the election commission's (EC) deputy secretary-general, announced that the EC has verified the last three MPs who can join in the voting for a prime minister at parliament.

Future Forward MP Srinual Boonlue won Sunday's by-election in a constituency in Chiang Mai province while Palang Pracharath MP Watanya Wongopasi and Democrat MP Chitpas Kridakorn were elected in party-list mode.

The House of Representatives consists of 350 MPs elected from constituencies and 150 MPs allocated to parties based on votes they received.

According to the EC, Tai Rak Tham Party leader Peerawit Ruangluedolapak, who was announced as an MP earlier, lost the seat when new figures from the constituency in Chiang Mai were added into the allocation formula.

The Future Forward MP has replaced Pheu Thai candidate Suraphol Kiatchaiyakorn, who won the March 24 election in the constituency Chiang Mai but was given an "orange card" on vote-buying charges.

The next step will be voting for a new prime minister by the House of Representatives and the Senate. The person who wins more than half of the total number of votes in both houses will be elected as prime minister.

All total 250 senators were selected by National Council for Peace and Order led by current Prime Minister Prayut Chan-o-cha.

With the support of Bhumjaithai Party, the pro-Prayut Palang Pracharath has some 188 seats in the lower house while the opposition seven parties led by Pheu Thai Party have 246 seats with one seat owned by Future Forward leader Thanathorn Juangroongruangkit suspended by Constitutional Court.