Quietly spoken and courteous, Trevor Sargent faces a tough challenge at the helm of the Greens - expected to lead but not to dominate an organisation which treasures its grassroots freedom.

For two decades and more, they have refused to be led, fearful that a cult of personality could emerge and threaten the desire to take decisions at the lowest possible level within the party. Today, however, life has moved on. An identifiable head is now seen as necessary if the party is to punch its weight in the battle for media coverage. Few politicians, though, are better prepared than Sargent for the role.

For years, he has travelled the length and breadth of Ireland by train and bus to talk to local branches and community groups, ready and willing to spread the environmental gospel.

"If elected, I would see myself as a rallying leader, not one who pontificates. I want to get the best out of every member in the party," he says, speaking in his sixth- floor office in Leinster House.

Unusually, perhaps, he attracts no ill feeling. Councillor Dan Boyle from Cork comments: "He is the party's conscience, a reluctant politician." Councillor Mary White from Carlow believes there is a "steely determination" about him.

Friend and fellow TD, John Gormley, with a smile, says: "He is a solid performer, not flamboyant, decent, reliable. He would have been the guy who would have been selected as school prefect."

Besides securing a better media profile for the Greens inside and outside the Dβil, Sargent will have to create some coherence inside an often-haphazard organisation, and he will have to do this without ruffling feathers.

The task will not be easy. Too often, the Greens speak with different voices. Last week, Leinster MEP Nuala Ahern approved of the Government's airspace offer to the US for the duration of the bin Laden crisis.

Dublin MEP Patricia McKenna took the opposing side. So, too, did Sargent. In fact, he was so determined that he ended up getting suspended from the Dβil for four days for his trouble.

Determination is one of Sargent's key characteristics. He showed it forcefully during his whirlwind romance with Heidi Bedell. He met her after he arrived late to a meeting. "Very quickly, I picked up that there was a very interesting person there."

Ten days later, he asked her to marry him as they were driven around Merrion Square in a horse-drawn carriage. She asked for time to think about it. Soon, he asked again. This time she said yes. "I knew what I wanted," he says simply.

The other defining characteristic is his sense of spirituality. A member of the Church of Ireland, Sargent does not preach or try to convert, but it is clearly important to him. "That is the battery driving my engine."

Today, he is involved with some fellow TDs who meet weekly for a prayer group in Leinster House and, occasionally, with counterparts - including some whom one might not suspect, such as the Rev Martin Smyth.

Born in 1960 in Templeogue, Co Dublin, to Harry and Mildred Sargent, he had, in his own words, "a safe and happy childhood", studying in turn at Rathfarnham National School and the High School in Rathgar.

In later years, however, tragedy struck. His younger sister, Cheryl, died at the age of 18 from lung cancer. "And she never smoked her life," he says, with a note of disbelief still in his voice.

His interest in the environment began early. Sitting at his bench in the High School, he spent time spotting the different types of seagulls feeding on the school's rugby pitch.

"Miss Williams, our maths teacher, established a young ornithologists club in which I got very involved. I lived for it. On Saturday mornings, we'd go out to Bull Island and the Booterstown marsh to watch."

Following secondary school, he began a three-year teaching degree aged just 16 years in the College of Education in Rathmines, which ran a course approved by Trinity College Dublin.

The degree, however, took four years. "I had studied Irish before, but the standard now was higher. I once asked the lecturer, Fiachra ╙ Dubhthaigh, if I could explain myself in English. He said 'No'. It wasn't confrontational - it was just that these are the rules. He has passed on since, God rest him."

Repeating a year, he immersed himself in Irish. Today, he is one of the Dβil's most fluent speakers. Last year, indeed, he complained vainly that TDs were not able to speak in Irish there because of the lack of translation.

Newly qualified, he headed for west Cork to teach in the Model School in Dunmanway, attracted by the chance of living in Ballingeary in the heart of the Muskerry Gaeltacht. In the beginning, the locals did not know what to make of the young Dubliner. "Often I can remember the parents not being sure whether I was a student or the teacher."

The 1980s recession quickly affected him. A family heading for Britain in search of work left him in charge of a house in Ballingeary and their collection of cats and dogs.

The experience was formative. Friends equipped with slash-hooks came annually to help him cut back the briars that threatened to smother the mile-long lane to the house. However, he never really settled.

"I did enjoy it, but I never was entirely comfortable because of the scarcity of people from Dublin. I felt I was a subject of suspicion as to what I was doing there."

Three years later, he headed back to Dublin. "My sister was very ill. That made me look out for a job in Dublin. A job came up in Balbriggan. I applied and I got it," he says.

The experience of the High School in Rathgar quickly resurfaced. "I had 16 pupils. I used to take them on nature walks. Once I met some elderly people on the beach. They asked jokingly, 'Are they all your own?'."

The desire for a life in tune with the environment strengthened. During his college days, he had written to all of political parties. The documentation which came back disappointed.

"I was struck by how short-term it was, how parochial, how it appealed to the short-term interests of voters. I did not find a global dimension anywhere," he says.

Later, one of his lecturers, Dr Kenneth Milne told him to read Fritz Shumacher's seminal work, Small is Beautiful: Economics As If People Mattered. He found a copy in a second-hand bookshop in Rathmines. The slow political climb began during the mid-1980s.

He ran for Dublin County Council in 1985. He got just 227 votes. In 1987, he won 2,000 votes in the general election.

The breakthrough came in 1989 during the European Parliament elections. He got 51,000 votes and came within striking distance of a seat. The decision to run had not been an easy one. "I knew if I ran that everything would change. I asked my next-door neighbour what I should do. He thought about it and advised against it. The next time we met he was down in the local having a pint and I was out canvassing," he says.

By 1992, he was in the Dβil in place of the Green's first TD, Roger Garland. Since then, he has quietly developed, leaving, perhaps, some of the rashness of youth behind.

Unhappy about the treatment of the Irish language, he made up his own car number-plates. The action landed him before the courts, where he received a £20 fine.

During a meeting of Dublin County Council in 1993, he produced a cheque from a property developer which had arrived in the Green Party offices complete with a rezoning request. His action created uproar. Some angry councillors manhandled him, an action that forced the meeting to be adjourned.

Later, he was arrested during a protest by Sellafield.

Today, he is "the safe pair of hands" alongside John Gormley's flamboyance. "Gormley often provides the flair, Sargent the steadiness. They work well together," says one observer.

The years have taught lessons. "I have learned that you have to be prepared for the long haul. I thought at 20 that change would come very quickly. Then, things got stuck in the doldrums. You have to wait for the wind to be behind you."

The Irish Times website, ireland.com, will report the Green Party conference over the weekend on its Breaking News service.