The 53-year-old Oscar winner's famous friends, including fellow actor Matt Damon and best friend Rande Gerber, gathered in the city ahead of the nuptials, and they came together for an intimate dinner at Da Ivo restaurant, which served as Clooney's bachelor party, reported E! online.
He was pictured surrounded by a large group of male friends on a boat holding drinks as they sailed down one of Venice's canals.
Alamuddin celebrated her bachelorette party separately with a party of her female friends and relatives, including her sister, Tala, and mother, Baria.
It will be followed by a star-studded luncheon on Sunday and a civil ceremony on Monday.