Kezia Dugdale has accused opponents of gender reforms of using "populist tactics" as MSPs prepare for a mammoth nine-hour debate.
The former Scottish Labour leader said the debate around the legislation has "been driven by and riven with fear".
Writing in a newspaper column she said: "Sadly, facts have been absent from much of this debate, which instead has fed on division and been driven by and riven with fear."
MSPs will discuss around 153 amendments to the controversial Gender Recognition Reform (Scotland) Bill today before a vote at Holyrood on Wednesday.
Scottish Labour Social Justice spokesperson Pam Duncan-Glancy has urged her colleagues to back changes in order for the Bill to work for everyone.
It comes as the First Minister has been warned of a "travesty of democracy" if the debate on Stage 3 of the Bill is time limited. Ahead of the session Social Justice Minister Shona Robison met with UK Equalities Minister Kemi Badenoch on Monday where the pair discussed the topic.
The Bill will make it easier for trans people to acquire a gender recognition certificate (GRC) by removing the requirement for a diagnosis of gender dysphoria.
It will also lower the minimum age for applicants from 18 to 16 and drop the time required for an applicant to live in their acquired gender from two years to three months - six for people aged 16 and 17 - though with a subsequent three-month reflection period.
Dugdale added: "This is classic populism, where for one to be strong another must be weak; for one group's rights to be enhanced another must be diminished; that I cannot be a feminist, a lesbian and still support trans rights."
"While I have written previously about what this proposed legislation does and does not do, I have resisted the temptation to enter the debate online or in the media, safe in the knowledge that the Bill had a parliamentary majority.
"It would pass, and so too, in time, would the fractious debate. But with hours to go, I feel that there is a need to call out the populist tactics at play and to defend the process and, indeed, the people this Bill is really about - the trans community - and their human right to live their lives with dignity and respect. And I do this as a lesbian and a defender of women's rights."
Ahead of the debate, Duncan-Glancy said: "Labour’s priority is to make this a bill both trans people and the wider public can have confidence in.
"We will always stand up for equality and human rights, and today we will continue working to bring people together and make this bill work for everyone.
"Our amendments offer real solutions to address the concerns people have about this bill, dealing with key questions on the Equality Act and single-sex spaces and ensuring the new process is properly monitored and reviewed.
"MSPs need to work together to protect human rights across the board and deliver a workable de-medicalised gender recognition process.”
Parliamentary officials have advised the consideration of amendments could take as long as nine hours - meaning parliament could sit close to midnight to consider the changes.
Tory MPS Rachael Hamilton, who is against the Bill, slammed the "time limit" on amendments in the debate. She said: "The SNP and Labour should have seen sense and backed our calls to delay the last reading of this Bill, to allow for full, reasoned debate on the concerns many of us have about protections for women and girls."
Following the meeting between Robison and Badenoch, a Scottish government spokesperson said: "We are pleased that this meeting with the UK Government has now taken place, following our letter of October. It gave the Social justice Secretary Shona Robison the opportunity to provide further clarification about what this Bill does, and importantly what it doesn’t do. For instance, she was able to reaffirm that this Bill does not change anything in the Equality Act, including exemptions.
"We also discussed how the Scottish Government has listened carefully to a wide range of feedback on the Bill as it has progressed through parliament, and has either made or supported a number of amendments at Stage 2 to strengthen it. We will do so again at Stage 3.
"Legal gender recognition is a devolved matter for which the Scottish Parliament can legislate. It is for other jurisdictions to set their policy on recognising legal gender recognition under current system. People who have already obtained legal gender recognition outside the UK can currently apply in the UK without providing medical advice.
"Scottish and UK officials have been meeting regularly to work together on cross-border issues – and there was an agreement that the two governments would continue to work together following the Bill’s final approval by MSPs.”
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