At least 10 Government MPs chose to abstain from Thursday's final conscience vote on same-sex marriage in the House of Representatives.

In the end there was no official record of the overwhelming support for the bill, because the Government benches were overflowing with Coalition, Labor and crossbench supporters.

Only four MPs voted no — the Coalition's Russell Broadbent, Keith Pitt and David Littleproud, and crossbencher Bob Katter.

Russell Broadbent and Bob Katter were among four MPs who voted no. ( ABC News: Matt Roberts )

According to the standing orders, if fewer than five people oppose a bill, it passes "on the voices" and the names of those who backed it are not officially recorded.

However, a number of staunch opponents of the same-sex marriage bill were notably absent during the vote.

Who abstained from the same-sex marriage vote? Barnaby Joyce (Nationals)

Barnaby Joyce (Nationals) Tony Abbott (Liberals)

Tony Abbott (Liberals) Andrew Hastie (Liberals)

Andrew Hastie (Liberals) Michael Sukkar (Liberals)

Michael Sukkar (Liberals) Kevin Andrews (Liberals)

Kevin Andrews (Liberals) Scott Morrison (Liberals)

Scott Morrison (Liberals) George Christensen (LNP)

George Christensen (LNP) Rick Wilson (Liberals)

Rick Wilson (Liberals) Stuart Robert (Liberals)

Stuart Robert (Liberals) Bert van Manen (Liberals) What about no votes? Bob Katter (independent)

Bob Katter (independent) Russell Broadbent (Liberal)

Russell Broadbent (Liberal) Keith Pitt (Nationals)

Keith Pitt (Nationals) David Littleproud (Nationals)

Deputy Prime Minister Barnaby Joyce was among those who abstained.

"I said at the start I believe in the current definition of marriage and I've said that all the way along," he told reporters in Sydney on Friday.

"But I said I'd never vote against the wishes of the Australian people and I didn't."

His frontbench colleague Scott Morrison was another high-profile member of the Government who elected to abstain.

Former prime minister Tony Abbott was also out of the chamber, along with Andrew Hastie, Stuart Robert, Michael Sukkar, Kevin Andrews, Rick Wilson, Bert van Manen and George Christensen.

Mr Christensen has been one of the loudest critics of the bill.

His electorate of Dawson voted 55 per cent in favour of legalising same-sex marriage.

George Christensen is seen outside the chamber during the same-sex marriage vote. ( ABC News: Matt Roberts )

"I told my electorate I would not vote against their wishes," Mr Christensen said to explain his decision to abstain.

"However I am concerned the same-sex marriage bill failed to protect religious liberty."

Prime Minister Malcolm Turnbull was questioned about Mr Abbott's decision to abstain rather than casting a vote.

Mr Turnbull said he did not notice his predecessor's absence.

"Well, it's a free vote," he said.

"You can vote against it or abstain if you wish."

Mr Abbott's Sydney electorate of Warringah was 75 per cent in favour of same-sex marriage, according to the postal survey.

Tony Abbott moved an amendment to the bill, but it was voted down. ( ABC News: Marco Catalano )

The ABC has sought information from the office of Government MP Alex Hawke, who also appears to have abstained from the division.

It is also unclear whether his Nationals colleague David Gillespie left the chamber before the vote, he is on an internal Coalition list of politicians who intended to abstain.

Stuart Robert has released a statement explaining his position.

"Mr Robert let the electorate know from the outset that he would personally be voting no in the postal survey, whilst also stating that if the electorate voted yes he would not stand in the way of a bill passing through the House."

His electorate of Fadden voted almost 62 per cent in favour of making gay marriage legal.

The 150-seat Parliament was already down to 149, with former member for Bennelong John Alexander fighting a by-election to win back his seat.

Labor MP Wayne Swan was absent from Parliament on Thursday attending a United Nations economic conference in Bangkok but his office has confirmed he planned to vote yes.