The milestone is especially sweet since Waters, a Queensland senator and co-deputy leader of the Australian Greens party, helped last year to extend Parliament's breastfeeding rules, according to The Independent.
While working moms were already allowed to breastfed in senate chambers, Waters fought for mothers — and fathers — to be able to care for infants while meeting on the senate floor.
Just before she returned to work this week, Waters told The Courier Mail she fully intended to make use of the new rule with Alia Joy.
"If she’s hungry, that’s what you do, you feed your baby,” said the senator.
The change comes eight years after Greens member Sarah Hanson-Young had her 2-year-old daughter taken from her arms and removed from the senate floor.
On Tuesday, Waters followed up the historic feeding with a jubilant tweet — and a call for more parents to join Parliament.
"So proud that my daughter Alia is the first baby to be breastfed in the federal Parliament! We need more #women & parents in Parli," she wrote.