The biggest names in fashion - including Donatella Versace, Tom Ford and Maria Grazia Chiuri - gathered in the Basilica of Santa Maria degli Angeli, a church designed by Michelangelo and built on the ruins of ancient Roman baths.
Valentino's co-founder Giancarlo Giammetti, dressed in a sharply tailored black satin suit, and the designer's last partner, Bruce Hoeksema, accompanied the plain wooden coffin as it entered the church, drawing applause from the crowds outside.
"Through him, I discovered beauty, a beauty that followed us throughout our lives, that has kept us busy. We met when we were kids, we dreamed the same dreams, we managed to realise some of them, I would even say many of them," Giammetti said in his eulogy.
In an improvised speech, Hoeksema said: "Valentino, you were the person I spoke to, not the person I spoke about. You were beside me when words were not needed. Life was not always perfect but it was real. One day at a time, for more than 40 years."
Mourners included Vogue's global editorial director Anna Wintour, actors Anne Hathaway and Elizabeth Hurley, US socialite Olivia Palermo and Valentino's current creative director Alessandro Michele and his predecessor Pierpaolo Piccioli.
Valentino's chief executive Riccardo Bellini, French billionaire Francois-Henri Pinault, Antoine Arnault, the eldest son of LVMH chairman Bernard Arnault, and Rachid Mohamed Rachid, CEO of Mayhoola, also attended.
The couturier, whose full name was Valentino Garavani and who built one of Italy's most celebrated fashion houses, died on Monday at his home in Rome, aged 93.
Hundreds gathered outside and inside the basilica, famed for the red of its marbled walls and columns - darker than Valentino red.
White flowers framed the altar and a black-and-white photo of Valentino stood next to his coffin.
There were flashes of red among the pews - hats, scarves, bright carmine coats and a woollen shawl.
More than 10,000 people paid their respects to Valentino on Wednesday and Thursday as he lay in state in Rome's Piazza Mignanelli, next to his fashion house's historical headquarters and a stone's throw from the city's iconic Spanish Steps.
There will be a private burial after the service.
with DPA
