"The national mean temperature was 0.83 degree Celsius above average, with a number of notable heatwaves during the year and record-breaking temperatures from October to December," the Bureau of Meteorology figures reported.
The combination of the most El Nino, a phenomena which sparks global weather extremes, in nearly two decades and background warming led to very warm temperatures globally throughout 2015 and contributed to Australia's warm year, the bureau said.
The World Meteorological Organisation has said 2015 is almost certain to be the warmest year on record globally. The El Nino also led to below average rainfall over much of eastern Australia.
Rainfall was well below average in southwest Western Australia, southeast South Australia, western to central Victoria, much of Tasmania and a large area of inland Queensland in 2015, the bureau said in an annual statement on climate.
The year started with a wetter than average January in large parts of the country but most of 2015 was drier than average across Australia. The bureau says Australian temperatures have warmed approximately one degree Celsius since 1950, consistent with global climate trends.