Lady Mone, which is her official title now, swore an oath of allegiance to the Queen in the traditional red ermine robe in a ceremony in the House of Lords which just took 4 minutes.
Welfare minister Lord Freud and Tory peer Baroness Morris of Bolton both accompanied her during the ceremony.
She was one of the 45 new peers that was announced by Prime Minister David Cameron in August this year. That same month Cameron named Mone as the country's entrepreneurship tsar, which means she will help people get people back into work in areas of high unemployment.
Mone posted on Twitter and Instagram about the day and even got a picture with UK Chancellor George Osborne and the Secretary of State for Work and Pensions, Ian Duncan Smith.
The ceremony marked an incredible milestone in Mone's rise to the top. Her life may look glamorous now, but it hasn't been plain sailing.
The Scottish founder of the British brand Ultimo, launched in 1996, grew up in an impoverished part of Glasgow, left school at 15 with no qualifications, and helped her family financially as a teenager after her dad became wheelchair-bound.
She even dedicated part of the ceremony to her father:
After leaving school she got pregnant at 18. Troubles followed Mone into her later life. She was mugged and assaulted outside her office, her husband left her on Christmas Day 2011, and her messy divorce cost her nearly half her wealth.
She's regularly pictured at glamourous events and never seems to have a hair out of place. However, she may want to rethink the picture she chose for the parliament website because she's inadvertantly promoting a wine company in the background:
