An Australian senator has resigned after learning she was also a Canadian.

Larissa Waters, who represented the Greens, said in a statement she was born in Winnipeg in 1977 to Australian parents who were briefly studying in Canada.

"I have lived my life thinking that as a baby I was naturalized to be Australian and only Australian, and my parents told me that I had until age 21 to actively seek Canadian citizenship. At 21, I chose not to seek dual citizenship, and I have never even visited Canada since leaving at 11 months old," the statement read.

It is with a heavy heart that I am resigning as Senator for Qld and Co-Deputy Leader of the Australian Greens. <a href="https://t.co/DuplaZPi2h">https://t.co/DuplaZPi2h</a> —@larissawaters

Waters, who was also a co-deputy leader of the party, looked into the status of her citizenship after another senator from the Greens resigned last week under the same circumstances.

Scott Ludlam, also a co-deputy leader, had recently discovered he also had New Zealand citizenship.

Australia's constitution states that a "citizen of a foreign power" is not eligible to be elected to Parliament.

"I had not renounced since I was unaware that I was a dual citizen. Obviously this is something that I should have sought advice on when I first nominated for the Senate in 2007, and I take full responsibility for this grave mistake and oversight," she said

Waters said other foreign-born lawmakers among the 226 in Parliament could find themselves in a similar predicament.

"There are many politicians in the Senate and the federal House of Representatives that were born overseas and it may well be that others have to make this embarrassing revelation as well," she told reporters.

"But I can hold my head up high knowing that the moment I found out, I have taken the step of announcing that I will sadly have to resign," she added.

Waters gained attention in May when she became the first woman to breastfeed in Australia's Parliament and has also done so while presenting a motion.

So proud that my daughter Alia is the first baby to be breastfed in the federal Parliament! We need more <a href="https://twitter.com/hashtag/women?src=hash">#women</a> & parents in Parli <a href="https://twitter.com/hashtag/auspol?src=hash">#auspol</a> <a href="https://t.co/w34nxWxG0y">pic.twitter.com/w34nxWxG0y</a> —@larissawaters

First time I've had to move a Senate motion while breastfeeding! And my partner in crime moved her own motion just before mine, bless her —@larissawaters

She regularly brought her daughter Alia to Parliament with her and was an advocate for making workplaces more family friendly.

Greens Leader Richard Di Natale said in a statement on his Facebook page that Waters had made an "innocent mistake."

He also said the party would review its processes for how candidates are vetted to "to prevent this from happening again."