SINN Féin president Mary Lou McDonald has said people should be "true to themselves" while discussing support for her eldest sibling's transition from male to female.
The Dublin TD revealed her sibling had transitioned last year in an interview with The Sunday Times.
Ms McDonald, who also has a younger brother and sister, said she supported her elder sister's decision to transition.
She told the newspaper: "Everybody gets one life, it’s not a dress rehearsal, so it’s important that people are true to themselves."
She added: "And of course, when it’s a family member, it’s all the more important because it’s so close to your life."
The TD was asked if she supported the recent transgender bill introduced in the Scottish Parliament, which allows for those aged 16 and over to change their gender designation on official documents without the need for a medical diagnosis of gender dysphoria.
The Gender Recognition Reform Bill has sparked controversy in the UK, after it was backed by MSPs in Edinburgh last month.
Scottish first minister Nicola Surgeon had hailed the passing of the bill at Holyrood as a "historic day for equality".
It has been revealed that the British government is considering blocking the legislation, despite gender recognition being a devolved matter, over fears it could impact on UK-wide equality laws.
Ms McDonald was asked during her Sunday Times interview if she could foresee Sinn Féin supporting similar legislation in future in the Dáil.
"We haven’t taken that step," she replied, adding that she, "like lots of people" was still "on a learning curve on these issues".