Marie Rimmer voted against a motion expressing confidence in the Government but could not stop it from passing in the House of Commons on Monday.
Unusually, the vote was tabled by the Government because it refused to accept the wording of a Labour motion after Boris Johnson announced he was staying on as Prime Minister until the autumn.
MPs were asked whether "this House has confidence in Her Majesty's government", with defeat almost certainly triggering a general election.
The St Helens South and Whiston MP voted against the motion, alongside the vast majority of her Labour colleagues, though it passed 349-238.
Voting against the motion were 181 Labour MPs, 37 SNP MPs, 12 Lib Dem MPs, two Independent MPs, one SDLP MP, one Alliance MP, three Plaid Cymru MPs and one Green Party MP .
Meanwhile, 342 Tory MPs, six DUP MPs and one Independent MP voted for it.
There were just 48 who abstained or did not vote – 16 Labour MPs, 12 Tory MPs, seven SNP MPs, two DUP MPs, six Independent MPs, one SDLP MP, two Alba Party MPs and two Lib Dem MPs.
The vote counts do not include the four MPs who acted as tellers, the seven Sinn Féin MPs who do not take their seats, the Speaker or the three Deputy Speakers.