The 22-year-old MP for Paisley and Renfrewshire South was the country's youngest elected MP since 1667.
As such, her Twitter account, which she's had since the age of 14, featured foulmouthed outbursts about Smirnoff Ice, Celtic and Oasis among the highlights, some of which have been deleted since she made her maiden speech.
And then, of course, there's this gem:
Mhairi's wisdom was called to the fore when she asked whether housing benefit cuts and the withdrawal of them for 18-21 year olds were punitive.
She argued that parents have no obligation to care for adults, and it could affect employment for young people should they be made unable to provide a permanent address:
Does the minister agree that it is simply ridiculous that young people should suffer purely because this government is obsessed with imposing austerity?
Her questions were waved away by Conservative MP Caroline Nokes, who said:
The Scottish Government already has a wide range of powers which would enable them to alleviate the changes being proposed here.
This response was clearly not to Mhairi's pleasure, as she tweeted the video of the exchange.
Yet more cuts that Scotland didn't vote for and no real answers from the Minister. https://t.co/CPhYFtYfcU
— Mhairi Black MP🏳️🌈 (@Mhairi Black MP🏳️🌈)
In the video, she appears to mutter the phrase:
You talk shite, hen.
People noticed and if anything they loved her for it:
"You talk shite hen" 1min13. Mhairi Black is too good for any of us. Too pure for this world. https://t.co/mlIuEvrzEC