Patrick Harvie hurries into his office, apologising for running late. He has spent the afternoon chairing a meeting of Holyrood’s transport, infrastructure and climate change committee that lasted almost five hours. Judging by the number of darkened offices, most of his fellow MSPs have left for the evening, but Harvie’s mind is still buzzing.

It’s a busy time for the man who was appointed leader of the Scottish Green Party yesterday in Edinburgh. As the only candidate, his promotion was never in doubt but, when we meet ahead of the vote, Harvie is coy. “I am quietly hopeful, but I don’t want to say more than that,” he says.

He is anxious I don’t use the word leader, preferring the party’s loony-left sounding title, co-convenor. “Greens are a bit touchy about the word leader,” he explains. “By and large, people in the Green party do not like to invest authority in a single figure. So my title, if I get it, will be co-convenor of the party’s council.”

The current co-convenor of the party’s council, Robin Harper, announced his decision to stand down earlier this year. Compared to his predecessor, a cheery veteran of the movement with a penchant for colourful scarves, Harvie, 35, is a young pretender and a sharp-suited one at that.

He was elected as a regional MSP for Glasgow in 2003 and again in 2007, when the number of Green MSPs fell from seven to two. He only joined the party in 2001 and must feel he has risen quickly through the ranks. “Well,” he says drily, “there aren’t many ranks to rise through in the Green party. We’re a very small organisation.”

His elevation also makes Harvie the first openly bisexual leader of a political party in Britain, an achievement that he acknowledges is less momentous than Barack Obama becoming the first black president of the US, but a milestone nonetheless. “It is less of an issue than it was, which is a good thing,” he says.

Before entering parliament, Harvie was involved with various organisations supporting lesbian, gay and bisexual young people. His interest in politics was sparked in 2000 by the Scottish executive’s move to repeal Section 28 of the Local Government Act prohibiting the promotion of homosexuality in schools. In the row that followed, Harvie discovered something in Scottish politics that was “important to me and my community”.

Harvie has never hidden his sexuality. He told his parents he was gay when he was 18. “My mother said, ‘don’t you think we already know that?’ It was a pretty positive response. It was actually a little harder to come out as bisexual a few years later, not so much with my family — I don’t remember ever having that conversation — but with people I worked with at the Gay Men's Project, where there was a sense that I should be identified as a gay man.

“It was something of the time, that you came out and identified yourself as gay, not bisexual. There was less fluid identity than there is now. As a society, we’re more grown up. People can be what they are, without labels.”

Growing up in Dumbarton, Harvie was academically gifted but awkward socially. “I kept to myself and I didn’t have a big group of friends,” he says. His father, a film editor, and his mother, a midwife, were early advocates of environmentalism. “My mother ran a recycling project in the mid-1980s. For part of my childhood, every Saturday afternoon was spent in the back of a van gathering up papers to be recycled. I also spent a lot of time at CND demos.”

Harvie’s mother, Anna, claims that her son told her at the age of 10 that he was going to be Britain’s first Green prime minister. Is that true? “She says it is,” he says. “I don’t remember.”

If he was withdrawn at Dumbarton Academy, Harvie blossomed once he got to Manchester Metropolitan University. “There is a very heavy expectation of heterosexuality at school and I didn’t learn how to relate. That all changed when I got to university.” He chose Manchester because of its vibrant gay scene. “I remember phoning the Lesbian and Gay Switchboard to ask what was on offer for gay students in Manchester and the guy I spoke to said he’d studied there and I’d have a good time.”

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