Wetang'ula and Marende were the only candidates cleared to seek the seat out of a pool of 37 applicants in a vote that gave the clearest indication of the numbers that the Kenya Kwanza Alliance and the Azimio la Umoja-One Kenya boast in Parliament.
Two candidates for the Speaker were disqualified on the basis that they had submitted forged signatures of their alleged proposers. Candidates for the position were required to have been supported by 20 MPs.
Azimio has suffered a series of defections, denting its position as the majority party in Parliament.
Voting in the first round lasted an hour, with sorting, counting and tallying taking the same time.
Earlier, Azimio MPs unsuccessfully tried to block Wetang'ula's candidacy, citing integrity issues, even as they said he had not resigned lawfully as Bungoma Senator.
Ruaraka MP TJ Kajwang' was the first to oppose the Ford Kenya leader's bid, raising what he termed a "fundamental constitutional issue."
"I have reliably learnt that the said candidate (Wetang'ula) resigned on August 9," Kajwang' said. "He tendered in papers to an office with no substantive holder given its occupant had already been elected as a governor."
The lawmaker argued that former Senate Speaker Kenneth Lusaka's term had ended by the time Wetang'ula was resigning as the Bungoma senator.
He also cited a resolution that barred the Ford Kenya leader from holding public office, courtesy of an integrity query during his tenure as Foreign Affairs minister.
Acting National Assembly Clerk Serah Kioko dismissed Kajwang's objection to Wetang'ula's candidacy, saying the former Bungoma senator had resigned on August 29 in a letter to Lusaka.
She said that the former Speaker still held the office, only relinquishing it yesterday as dictated by the Constitution.
"He communicated, in writing, his decision to resign as the senator-elect for Bungoma," Kioko said. "I am satisfied that Wetang'ula is qualified for election as Speaker."
Other lawmakers had also weighed in on the matter, with Kikuyu MP Kimani Ichung'wa saying that the Ford Kenya leader's resignation was lawful.
"Its not true that Wetang'ula resigned on August 9. He resigned two days after the gazettement of Senators," stated Ichungwa. "Its not also true that the office did not have any substantive holder given that the office operates in perpetuity until after another speaker is sworn in."
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Garissa Township MP Aden Duale held the same view, arguing that the former Bungoma senator did not need to resign as he had not taken the oath of office.
"Wetang'ula ceased to be senator for Bungoma on August 9. From that date to this afternoon, Wetang'ula is a senator-elect and is under no legal obligation to resign," Duale said. "Resign from what?"
On whether or not he had failed the integrity test, the Garissa Township MP said that investigative agencies had cleared Wetang'ula over alleged involvement in corruption dealings when he was a minister.
Nominated MP John Mbadi said there was need to amend the Constitution to exempt MPs from resigning before seeking to contest for the Speaker's position.
"This matter can't be wished away because we have an issue and there's a grey area on the law requiring members to resign before contesting," he said.
Some 348 newly-elected MPs of the 13th Parliament took their oaths of office before voting, an event that was attended their families.
By the time of going of press, voting for deputy Speaker was underway, pitting Uasin Gishu Woman Representative Gladys Boss against Dadaab Member of Parliament Farah Maalim.