Ledger's father, Kim; mother, Sally Bell; sister Kate and half-sisters Ashleigh and Olivia all attended the event Thursday at the Indiana Tea Room on Cottesloe Beach, the site of the wake held last year after Ledger's funeral.
Ledger, who earned an Oscar nomination Thursday for his role as the Joker in "The Dark Knight," died Jan. 22, 2008 of an accidental prescription drug overdose. He was 28.
In addition to his parents and siblings, Ledger is survived by Matilda, his 3-year-old daughter with his former partner, actress Michelle Williams.
"Michelle is doing an amazing job with 'our girl' and together we will cherish every moment of her steps through life," People.com quoted Kate Ledger as telling reporters before the family luncheon.
Ashleigh Bell recalled her brother saying he had "the time of his life" playing the Joker.
"Although we would love to have him here with us, we are so proud and so excited on his behalf," Ashleigh told reporters. "We will take this opportunity today to honor his wonderful life and take comfort in knowing Heath will continue to touch future generations through this amazing art form. ...What an unbelievable legacy he has left for Matilda and our family."