Farrell had become close friends with the three-time Oscar winner in recent years. Taylor died of congestive heart failure March 23 at age 79.
Actor Michael Caine, singer Elton John, Taylor's children Michael and Christopher Wilding, Liza Tivey and Maria Burton, and Taylor's stepdaughter Kate Burton were among the 400 guests at Sunday's 75-minute tribute to the star of "Who's Afraid of Virginia Woolf?" "Cat on a Hot Tin Roof," "Giant," "Father of the Bride" and "National Velvet."
"To say that the world got smaller, emptier, darker and lonelier when we lost Elizabeth is an understatement," People.com said John told the crowd. "She was a true rock, a pioneer, a pathfinder, a trailblazer and a star who will always burn bright and always had time to laugh at herself."
The recording star closed the memorial by singing "Blue Eyes."
Taylor won the best actress Oscar for "Butterfield 8" in 1960 and "Who's Afraid of Virginia Woolf" in 1966. She received the Jean Hersholt Humanitarian Award in 1992.