Baroness Davidson of Lundin Links wore the traditional scarlet robes for the short introduction ceremony in which she swore the oath of allegiance to the Queen.
She was flanked by supporters Lord Keen of Elie, the former Advocate General for Scotland, and Lord McInnes of Kilwinning, who recently announced he was stepping down as director of the Scottish Conservatives to advise the Prime Minister on the Union.
Her title comes from the village in Fife where she grew up and her parents still live, according to the party.
The 42-year-old, who served as an MSP from 2011 to 2021 and stood down as leader in August 2019, is the fifth former Scottish leader to be appointed to the Lords.
She has said her role would involve “making sure all UK-wide laws are fit for purpose” and that her areas of particular interest include gambling reform, end-of-life choices, and “reforming the House of Lords into a democratic chamber”.
Earlier this month, Lady Davidson said there was “not a chance” she would become Prime Minister Boris Johnson’s next Scottish Secretary, and commitments to her family mean she will not take on any “big jobs” until her son is in school.
She became the first UK party leader to give birth in office when she had baby Finn in October 2018 with her partner, Jen Wilson.
A SNP spokesperson said Ms Davidson had “sold out” by accepting the position, adding: "The ex-leader once responsible for a Scottish Tory operation to keep Boris Johnson out of Downing Street has now completely sold out, bought off by the Prime Minister's gift of a lucrative lifetime seat in the Lords.
"The Baroness has been talking a good game about being independently-minded and outspoken from the red benches, but no-one believes it. She is simply trying to justify her actions.
"For her own financial gain she is perpetuating an archaic and undemocratic system … the Lords should be scrapped and Baroness Davidson should hang her head in shame for participating in such a democratic outrage."