The so-called “meaningful vote” will take place later this evening following five days of controversial debate on Brexit.
Mrs May has called for politicians to back her deal but it is widely anticipated she will be defeated, with many of her own MPs expected to join opposition parties to vote against her deal for leaving the European Union.
Falkirk MP John McNally said: “My SNP colleagues and I will vote against Theresa May’s deal tonight.
“This deal would drag Scotland out of the EU against its own will. It puts environmental protections that we have tirelessly worked for at great risk. Scotland is a proud European nation and voted to remain as one.”
He added that, following discussions with various other MPs he believed Mrs May faces a “resounding defeat” this evening.
“I am no futurologist, but the intentions and indications are that most of the members, whether a leaver or a remainer in all parties are unhappy about the whole manner of the way the PM has conducted this vital decision, this crucial decision that affects everyone’s everyday lives,” Mr McNally said.
“That intransigence will result in a humiliating defeat for her government.”
Linlithgow and East Falkirk MP Martyn Day said he too would be voting against the PM’s Brexit deal tonight.
“Theresa May’s deal would have multiple negative impacts for Scotland and the rest of the UK,” he said.
“There are evident economic issues, like how the loss of European funding will be addressed and how the economy will be affected if we leave the single market and customs union.
“It also fails to guarantee key rights such as human, environmental and employment rights which Scotland needs and wants.”
Voting will start at 7pm tonight, with the result expected to be announced at around 9.15pm.
Labour is then expected to raise a point of order at 9.30pm to announce it intention to table a formal vote of no confidence in the government, with the vote to be held on Thursday.