Less than a week after Scott Ludlam resigned from Parliament, Larissa Waters, another Greens senator, has quit after revealing she is ineligible to sit in federal Parliament because she is a dual citizen.

Senator Waters was born in Canada to Australian parents and came to Australia with her family as an 11-month-old, but has never renounced her dual citizenship, making her ineligible to serve. Nor has she ever returned to Canada.

Compounding the crisis for the Greens is the role Senator Waters held. She was the co-deputy leader of the party, a position she shared with Senator Ludlam.

The Queensland senator dropped the bombshell only days after Senator Ludlam resigned after realising he held dual citizenship with New Zealand.

Both resignations mean the Greens have lost two of their strongest parliamentary performers in just five days, and comes at a time of tense in-fighting within the party.

Her resignation also means the party faces two senate recounts – in Queensland and West Australia – with former leader of the Australian Democrats, Andrew Bartlett, in line to take Senator Water’s Senate spot.

A tearful Senator Waters, who has held a Senate seat since July 2011, told a press conference in Brisbane on Tuesday she was devastated by the realisation she held dual citizenship.

Senator Waters explained that her parents had briefly studied and worked in Canada before returning to Australia where she was naturalised.

Her parents had advised her she had until age 21 to seek Canadian citizenship, but never did so and thought the matter had ended there.

“However after Scott’s shock discovery, I immediately sought legal advice, and was devastated to learn that because of 70-year-old Canadian laws, I had been a dual citizen from birth, and that Canadian law changed a week after I was born and required me to have actively renounced Canadian citizenship.

“It is with a heavy heart that I am forced to resign as Senator for Queensland and Co-Deputy Leader of the Australian Greens, effective today.

“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. I am deeply sorry for the impact that it will have.”

Senator Waters apologised “wholeheartedly to all those who have supported me and helped me to become a representative for the wonderful people of Queensland over the last six years”.

Greens Leader Richard Di Natale said he was “gutted” by the resignation and commended the senator as a “force of nature” during her fight against Queensland’s Adani coal mine.

“I am sad to see Larissa go but I know she will be back,” Senator Di Natale said, adding that her demise was the result of an “innocent mistake”.

Senator Waters was seen as a bright light in the party and had been touted as a future party leader. She made global headlines earlier this year when she became the first woman to breastfeed her child in the federal Parliament.