Gentiloni will meet with Brexit negotiator Michel Barnier at 4pm on Thursday afternoon, according to a government statement which said the meeting would take place at Palazzo Chigi, the prime minister's official residence,
It comes a day before May's big speech, which will take place in Santa Maria Novella, according to a statement from the organization responsible for preservation of the site.
È ufficiale, Theresa May ha scelto Santa Maria Novella come prestigiosa sede per il suo discorso sulla Brexit domani. pic.twitter.com/auMiD8v0ez— santamarianovella (@operasmn) September 21, 2017
The 13th-century church is the oldest of Florence's major churches, and located conveniently close to the city's train station. It is famed for its cloisters and chapels which house elaborate frescoes.
May's speech is set to take place at around 3.30 pm, and the prime minister does not have other official engagements while in Italy.
Asked about the choice of venue when the speech was announced one week ago, May's spokesperson said: "The prime minister wanted to give a speech on the UK's future relationship with Europe in its historical heart.
"The UK has had deep cultural and economic ties spanning centuries with Florence, a city known for its historical trading power."
Florentine mayor Dario Nardella said the choice was a recognition of the city's "important historical role".
However, observers have pointed to other parallels between Florence's history and the future Britain could face post-Brexit.
TheCityUK, a British finance lobby, warned in a statement that "Florence was once a powerful European financial centre, but lost its position as other better-connected centres arose elsewhere" and said it did not want to see UK face the same fate.
Global banks have already begun moving their headquarters and many jobs from London to other European cities, with Frankfurt emerging as one of the big winners.
Florence is also known as the hometown of the Guelphs and Ghibellines, arguably the first political parties in Europe, as well as of poet Dante and former prime minister Matteo Renzi.