Candidate Maggie Chapman, who grew up in Zimbabwe, wants Scots to reject what she called the “politics of fear” put forward by Ukip.
The two parties occupy opposite ends of the political spectrum but are both vying for the sixth and final seat to represent Scotland in the May 22 poll.
Three separate opinion polls taken in April suggest Ukip has more support, putting them as high as 10%, compared with the Greens at a high of 6%.
Ms Chapman compared the different approaches of the two parties at the Greens’ official European Parliament election launch in Edinburgh.
“Who wins the European election will send a message about the kind of Scotland that we want, the kind of priorities that Scots have for our country,” she said.
“A vote for the Greens, a vote for us, signals a vote for the politics of hope.
“We choose a just economy, a welcoming country, a nation of peace - not the opposite, the notions that Ukip stands for, the politics of fear which marginalise people, which divide people. That is not the kind of Scotland in Europe that we want.”
Green co-convener Patrick Harvie, a Glasgow MSP, went further by branding Ukip racist.
“Most people don’t want to vote for a racist party, and it’s important that the true values of a party like that are exposed and that people understand what it really represents,” he said.
Ukip leader Nigel Farage is expected to formally launch his party’s campaign in Edinburgh tomorrow.
Mr Farage wants to take a united Britain out of the EU while the Greens support the campaign for an independent Scotland as a full EU state.
Ms Chapman, who is a councillor in Leith, Edinburgh, works as a lecturer at Napier University.
She drew on her background, saying: “I came to Scotland in 1998 and have chose to make this my home ever since. I cannot imagine living anywhere else.
“For the last seven years I’ve represented the people of Leith in Edinburgh as their local Green councillor and I’ve worked in the universities of our capital where I see daily the enormous benefit to our economy, society and culture that institutions which welcome staff and students from across the world bring.
“When I say I passionately believe that the movement of people between countries is good for our society, good for our economy, please believe that I mean it.”
The Green manifesto pledges opposition to Nato membership, wants more reliance on renewable energy and wants to put public services such as railways in public hands.
Ms Chapman said an independent Scotland would be able to make a difference in the EU.
“It’s not about nationalism,” she said.
“I’m as interested in workers in Scotland, in Edinburgh, in Leith, as I am in the rights of workers of Portugal and Spain.
“Europe gives us the opportunity to co-operate on things that should be European wide.”
Greens pioneered limits on bankers’ bonuses, she said.
The other main parties in Scotland have already launched their campaigns.
Labour leader Johann Lamont said the campaign should not be seen as an extension of the referendum campaign.
First Minister Alex Salmond said that Westminster representation in the European Union had ‘’let Scotland down time and time again’’.
Liberal Democrat candidate George Lyon says his party offers genuine support for the UK and for EU membership.
Some commentators suggest a drop in support for the Lib Dems puts the Greens or Ukip in contention for a seat.