Lady Gaga is expected to address around hundreds of thousands of marchers at Rome Pride on Saturday.
The singer, who is considered the world’s best-known gay rights advocate, will sing her hit single Born This Way.
Rome is hosting Europride. Organisers say they expect one million participants, while police estimate that 500,000 will join the march.
Italy does not have hate crime legislation and gay couples cannot marry or adopt.
Prime minister Silvio Berlusconi is on record for opposing gay rights, although gay campaigners claim his alleged affairs with minors make him a hypocrite.
Last year, the Italian leader brushed off criticism, saying: “It’s better to be passionate about beautiful women than to be gay.”
Paolo Patane, the director of gay campaign group Arcigay, told AFP: “This is the most backward government Italy has had since World War II.
“It’s a government in which the prime minister goes with underage girls but then says that parliament will never approve legislation that contradicts the concept of the family promoted by the Vatican,” he said.
Marchers will proceed from the city centre to the Circus Maximus for a rally and concert.