Gianotti rode into Ivrea, north-west Italy, on Sunday after a 29,430km tour taking 144 days.
“The most beautiful finish line of my life!” she wrote on Facebook after arriving to crowds of supporters.
Gianotti broke the world record set by Juliana Buhring, a British-German cyclist, who toured the globe in 152 days two years ago.
The 32-year-old Italian completed the tour despite having an accident in the US, prompting her to put the tour temporarily on hold, Gazzetta dello Sport said.
A sports enthusiast, Gianotti had been living in the village of Montalto before taking up the cycling challenge.
“Because of the economic crisis, my business closed and I said, ‘It’s now or never’. I rolled up my sleeves and began to plan the adventure,” she was quoted in Gazzetta dello Sport as saying.
She won €45,000 sponsorship from ten companies, after contacting 2,500 businesses. The high costs included a €20,000 campervan for Gianotti and her team to sleep in, plus €10,000 in flights for the group of three, the newspaper said.