Plans to develop the North Sea field – which is estimated to contain up to 300 million barrels of oil – have been submitted again by owners Equinor.
However, Ms Mackay told the Scottish Green Party conference in Edinburgh: “We have to be the party that calls out the lies of big polluters.”
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Ms Mackay, who was elected co-leader with fellow MSP Ross Greer in August, told her fellow Scottish Greens: “Drilling for new oil and gas in fields like Rosebank will do nothing to lower energy bills or protect our planet.
“It is pure climate vandalism and we have to stop Rosebank.”
Development of the oil field, which lies 80 miles west of Shetland, had been approved by the Conservative government in 2023 but that decision was challenged in the courts in the wake of a Supreme Court ruling which said the emissions created from burning fossil fuels should be considered when granting permission for new drilling sites.
Her comments came as Zack Polanski, leader of the Green Party of England and Wales, insisted the UK is “one of the most nature depleted countries in the world”.
Addressing protesters in London, Mr Polanski said: “The very least this Government need to do is to stop making things worse.”
Ms Mackay also used her conference speech to hit out at the UK Government over the closure of Scotland’s only oil refinery in Grangemouth.
Hundreds of jobs were lost after owners Petroineos closed the refinery earlier this year, with Ms Mackay, who grew up in the area saying: “I’m sick of governments and corporations using tags like ‘just transition’ as a cheap slogan.
“What happened in Grangemouth is not a just transition.
“Our communities don’t need empty words, words don’t pay the bills, or put food on the table.
“They need real plans to provide real jobs and real opportunities.”
Ms Mackay insisted: “That site could have been saved. Labour promised to save it – they promised £200 million – and the message from the workers is clear: show us the money.”
She said that the Grangemouth plant “could have been nationalised”, adding: “We cannot leave the future of our communities in the hands of billionaires who are all too happy to abandon us when the money dries up.”
With the Scottish Greens having set the target of overtaking Labour in May’s Holyrood ballot, Ms Mackay said her party was “on the verge of a historic election” with the “chance to elect more green voices than ever before”.
She also told how the birth of her first child, Callan, in June meant she had “never felt more committed to building a greener Scotland”.
She joked that she was speaking at Saturday’s conference “in relatively one piece, without too much baby dribble on me” as she said the Green model, with two co-leaders at the helm, had allowed her to take on the challenge.
“In other parties there would have been a whole load of barriers to a new mum being elected to a leadership role,” Ms Mackay said.
“It is only because of our co-leadership model and the support of ordinary members, I have been afforded this opportunity.”
She continued: “The support I have had says something about our party and the values we stand for.
“When I think about the country I want us to be, it is one where we support each other, one where we lift each other up and one where we do things differently.”