 It can do so by amending the definition of "marriage" in the "Marriage Act", which it did in December 2017.According to the Australian Bureau of Statistics, 6,538 same-sex couples married in Australia in 2018, the first full year in which same-sex couples could lawfully marry in the country.As 119,188 couples were married that year, same-sex unions accounted for 5.5% all marriages.