Was Edmund Barton the longest serving prime minister of Australia?

No, Edmund Barton was not the longest serving prime minister of Australia. He served as the first prime minister of Australia from 1 January 1901 to 24 September 1903. The longest-serving prime minister of Australia was Robert Menzies, who served for a total of 18 years, 2 months and 18 days across two separate terms from 1939-41 and 1949-66.