She is calm, groomed, and virtually unflappable. She has a sharp intellect. She is a forensic Senate operative in the John Faulkner mould. She is a lesbian. She is a practising Christian. And now she is one of Kevin Rudd's most senior cabinet ministers, charged with driving an international consensus on climate change, and a domestic consensus on water management.

It's a huge ask, by anyone's standards. Penny Wong did not always intend to be a politician, even if it looks that way in retrospect. Her initial plan was to be a doctor, and to work for Medecins Sans Frontieres; she won a spot in medical school in 1986, deferred it, and then left for an exchange year in Brazil, where she volunteered at a hospital - and quickly changed her career plans. "There was a bit of a problem with blood," she explains briskly.

This is an important revelation, as it might be the first and last recorded example of squeamishness in Penny Wong. Arriving at the University of Adelaide in 1987 as a first-year arts student, the politically conscious Wong dabbled with a couple of environmental groups and the left-wing group CISCAC - the Committee in Solidarity with Central America and the Caribbean.

(This group was founded and run, incidentally, by fellow arts student and enthusiastic campus Trotskyist David Penberthy, who has since moved to the beating heart of Australian conspicuous consumption - Sydney - where he edits The Daily Telegraph.) Pragmatic Wong, however, was never going to be a very committed Trotskyist. In 1988 she swivelled her gun turrets towards the Labor Club, which had been colonised two or three years earlier by George Karzis, a cheerful right-wing headkicker who has since worked in senior advisory roles for state and federal Labor politicians. "I ran it as a non-factional group," recalls Karzis from his Adelaide legal office, breaking off to laugh uproariously before adding: "That is, there was no other faction than mine. "Penny arrived in 1988. By the following March, she had organised the numbers and there was the largest ever Labor Club meeting - the union theatre was packed to the rafters. It was an unfortunate display of branch stacking - by both of us. She was trying to take the club over and I was trying to defend it. And she won! I have to concede, I backed the wrong horse."

Wong remembers: "We had these big fights about who would control the Labor Club. I mean - really. Look, I think with the benefit of hindsight we probably got much more wound up in student politics than we really needed to, but isn't that what you do when you're young?" It's true that in student politics, where practitioners subsist on a rich diet of reality-free political theory and too many standing orders, things can often get out of hand.

What you tend to end up with is a riot of ballot-stuffing, vote-rigging, dirt-digging and amateur character assassination, washed down with endless schooners of beer. The thing about Penny Wong, however, is that few such tales of outright excess exist. "To her credit, there are no funny stories involving Penny Wong," is how one alumnus of the vintage puts it.

Another - her former Labor club colleague Amy Barrett, who is now a lawyer in Sydney - says Wong was not given to skulduggery. "The rest of us would be running around, putting up posters, but she would be talking about serious number-crunching deals, preference flows, stuff that made you think - this is really serious business," she says.

Wong called people "comrade"; she was intensely organised; her attention to detail was rigorous. If a comrade was spending long hours campaigning, Wong might arrange for a set of course notes to materialise in that person's pigeonhole, just so they didn't get too behind. "She was totally focused on politics, right from when she started," says Kris Hanna, another comrade who ended up in the South Australian Parliament - he now serves as an independent, having defected from Labor several years ago. "She was methodical, serious and committed - in the left, she was known as 'Penny the Prefect'."

In fact, Wong's generation of Adelaide university student politics produced an aberrantly large crop of professional politicians. Senator Natasha Stott Despoja was a contemporary, as well as Wong's then boyfriend, Jay Weatherill, now a senior minister in Mike Rann's South Australian Government. Other contemporaries include the South Australian Transport Minister, Pat Conlon, the federal Liberals Christopher Pyne and Andrew Southcott, the Labor senator Anne McEwen, the new member for Port Adelaide, Mark Butler, and the South Australian Speaker, Jack Snelling. Wong worked part-time as an organiser for the Construction, Forestry, Mining and Energy Union through the concluding stages of her law degree, but still managed to graduate with honours.

She formed a deep alliance with the "Bolkus Left" - a sociable grouping of ambitious youngsters around the then senator Nick Bolkus, who was a mentor to Wong and whom she thanked in her maiden speech in 2002. Conlon, Butler, Weatherill and Wong were the most promising of Bolkus' proteges, and all are still on the rise. But the group suffered a wrenching split in 2003, on the matter of Bolkus's own future in the Senate. He wanted to stay on, but was defeated by a coalition of friends and foes. Wong's failure to defend her mentor caused some hard feelings, which persist in South Australia to this day.

"Penny's made a lot of sacrifices to get where she is. Mainly of other people," says one party to that upheaval. Her defenders say this attitude is unfair, and that Wong, already in the Senate, did not advance at Bolkus's expense; Bolkus declined to comment this week. Certainly, Wong is known widely within the party for her driving ambition, and her lack of squeamishness about the hard and unattractive side of factional business, of which she saw plenty through the Crean/Latham era. "She is very into the politics. But she has a sort of dignity and authority about it," Hanna says.

Like Julia Gillard (a friend), Wong has answered internal critics with the most crushingly effective retort available in politics - performance. Butler, who remains factionally close, describes her as a cool political operator ideally suited to the task set for her by Rudd. Butler is the former secretary of the Liquor, Hospitality and Miscellaneous Workers Union in South Australia; he has also served on Labor's national executive committee and is viewed as an exceptional talent federally for Labor (a fact which would no doubt have puzzled his great-grandfather, the 1920s Liberal premier Sir Richard Butler, were he still around). Wong worked for Butler as a legal officer for three years at the union before she won Senate preselection, and was a barrister and solicitor at the Adelaide firm Duncan and Hannon for three years before that.

Butler says she has a forensic brain and a gift for cross-examination; he describes her appointment as a "brilliant" move on Rudd's part. "Climate change, water, emissions trading - they're all about getting across some really difficult technical detail, then getting into a room and negotiating hard. They are just her major strengths," he says. Wong's negotiating skills were proven in 2003, when as a new senator she wangled affirmative action rules through the federal party during the infamous "special rules conference" called by Simon Crean.

Conlon, whose relations with Wong are chillier since the split, nevertheless describes her as "intelligent, and focused on her goals", and says he has "no doubt at all that she will be a success in the role". As a politician, Wong is not naturally gregarious; at least, not to the degree that many of her colleagues are. She is serious of demeanour and conservative of appearance, given neither to drinking nor excessive frivolity.

A periodic flirtation with cigarettes is about as close as she gets to formal vice. Mark Latham, who met her in 2000 at Labor's national conference in Hobart, made a spirited attempt to have her referred to thenceforth as "Wongy". It didn't catch on.

But in private she has a warmth and humour which belies her reputation; there is a touch of goofiness, if you can imagine that. There is a hint of it in her smile, which is shy and engaging; she is striking to look at, and photogenic, but hates having her picture taken. Over the course of last month's election she served as Labor's federal campaign spokeswoman, proving to be articulate and surefooted; on being asked anything about her private life, however, she gets tongue-tied. She seems genuinely puzzled by the idea that anyone would be interested in the fact that she is Australia's first lesbian cabinet minister, and the first Asian-born cabinet minister, for that matter.

"If it means that we … as a nation … if it shows that we are a nation where people can achieve things just on their abilities, then it is a good thing," she says, with rare hesitance. Wong brought her mother, Jane Chapman, and her partner, Sophie Allouache - a former University of Adelaide Students' Association president - to Monday's swearing-in ceremony at Yarralumla.

"Is she out?" wondered her old comrade Barrett, with interest, when contacted this week. Technically, Wong was never really "in". She has never sought to disguise or advertise her sexuality, which - after her undergraduate experimentation with the opposite sex - has long been settled in its present orientation. When Wong won preselection for the Senate before the 2001 election (she replaced the retiring Keating government veteran Rosemary Crowley), the joke went around that she would never have been able to contest a lower house seat, being not only a woman, but Asian and gay to boot. Wong gently disagrees, but says she never thought of a House of Representatives seat in any event: "I actually think that the house of review is the chamber where more detailed legislative work is done."

Nevertheless, she has made some references in the past to the marginalisation she and her younger brother, Toby, experienced while growing up in Adelaide, and her maiden speech was a passionate denunciation of the politics of racial division. The two young Wongs moved from Malaysia to Adelaide with their mother when Penny was eight; their father remains overseas, though he and Penny keep in touch.

Toby, a bright and charismatic boy, went on to work as a chef in Adelaide while Penny pursued her political career. Toby turned 30 on the day his sister was elected to the Senate in 2001, in the middle of the bitterest race election this country had seen in the course of the siblings' lives. Ten days later, he took his own life. Wong does not discuss the circumstances of this dreadful blow, beside an enigmatic promise to him in her maiden speech: "Your life and death ensure that I shall never forget what it is like for those who are truly marginalised."

She leaned heavily on her faith after her brother's death, and remains a committed worshipper in the Uniting Church, although religion is another subject she is loath to discuss. "It's a very private matter. I suppose I think people have very different ways in which they express their spirituality. I have mine. It's deeply personal, and it has sustained me at difficult times of my life." On her brother: "The only thing I'd want to say is how much I missed him the day I was sworn in."

The reporter is also a University of Adelaide alumnus.