It's 10.05pm on a rainy Tuesday night in the MSNBC studio in the now famous New York address, 30 Rock, and Rachel Maddow – one of the highest profile news anchors in America and certainly one of the most popular with liberal viewers – has just finished another edition of her nightly eponymous prime-time show.

Instead of regurgitating the pervasive but ultimately low-impact tales that make up the menu of so much TV news coverage in America (Donald Trump, Tea Partyists, etc etc), Maddow focused on stories that both affect people and require hard-nosed reporting, such as how the Republican party is trying to make it harder for people to register to vote in the upcoming election, and why (hint: 68% of first time voters in the last election voted for Barack Obama.)

She presented it all with her usual mix of intelligence, empathy and arch humour, and while she might have been missing the helmet of blond hair and rictus smile – uniform for most American female newscasters – she was wearing the de rigueur tailored jacket.

However, Maddow is an anchor who is, she says later, spitting out the newly learned word, "definitely not an 'autocutie'". And if there were any doubt, when she stands up from her desk, she reveals that the jacket is worn, not with a pencil skirt, but a pair of jeans and cumbersome black and red trainers. "And not just jeans – ugly jeans!" Maddow laughs, proudly, and then swiftly swaps that regulation jacket for a grey sweatshirt.

Sly jokes

In the three years since Maddow was given her own show on MSNBC, having spent the early part of her career on radio and "doing the talking head thing", many have tried to explain her popularity and most have homed in on what she is not – namely, one of the interchangeable blustering, middle-aged white guys who host American news programmes. She is, instead, a youthful, easy-tempered, gay, 38-year-old woman who prefers sly jokes to spittle-flecked anger.

Jon Stewart notably omitted her from his criticism of other leading newscasters who, he claimed at his Rally to Restore Sanity in Washington DC last year, drag down American political debate with their hyperbole and hysteria. Instead, he gave Maddow a long interview respectfully explaining the rally, confirming the high esteem in which he holds her.

"I'm not a screamer," she agrees after the show during a chat in her office, her legs curled up underneath her, and contacts swapped for heavy-framed geekish glasses. "I'm confrontational, but I don't think that translates into anger." What it translates into is ratings. In the first quarter of this year, Maddow's ratings were 26% higher than CNN's talkshow in the same timeslot (1,065,000 to 848,000), which, incidentally, is hosted by Piers Morgan.

But with success comes attention, good and bad. Some have claimed she is too arch. David Frum, a former speech writer for George Bush, informed her in 2008, on her show, that she was part of "the ugliness that has been a feature of American politics in the past eight years". (Maddow's calm response pretty much refuted the charge.) Her name has acquired totemic meaning for politicians on the right who have cited her in speeches as a bogeyman, even though she has never and, she promises, will never run for office: "I'm just like, really, am I the scariest thing you can conjure?" Maddow laughs.

She was also referenced, fondly, on the sitcom 30 Rock, when Alec Baldwin announced "I have to talk to Rachel Maddow – only one of us can have this haircut." Maddow winces slightly at the insinuation that she is now a celebrity, but she does concede "it got me more pop culture cred from my friends than anything, ever".

Whereas in Britain the newspapers are openly partisan and the TV news is expected to be politically neutral, in America it is the reverse, at least on the cable networks. Fox News is the most notorious example of nakedly political cable news and MSNBC represents the other end of the political spectrum. And Maddow insists this is no bad thing: "I think a lot of people of my generation are discomfited by the assertion of neutrality in the mainstream media, this idea that they're the voice of God. I think it's just honest to say, yes, you know where I'm coming from but you can fact-check anything I say."

Of Fox News, she says simply "When it starts to seem like you have popped into bed with a specific party, it makes it difficult for people to believe you are not doing someone else's bidding for them."

At MSNBC, on the other hand, "there are people here who are identified as liberals, but there is no political agenda".

Despite the thrill she gets from "connecting the dots in a story", she had never considered journalism until friends dared her to try out at an open mike audition for a local DJ job in her 20s, which she got.

But she did have a journalistic idol when she was growing up: "I always really admired Jessica Mitford. That whole expose of the American funeral industry [Mitford's book, The American Way of Death] was so cool to me because it was so uncompromising and tough, but done in this witty and interesting way. And for her to have come from that family and take such an outsider's perspective, that just seemed so great."

These are all descriptions many would apply to Maddow – she is writing a book about a similarly unfashionable subject: American politics and the military.

Maddow grew up in California in a "very conservative, nasty little town". She realised she was gay in her teens and came out a few months later at Stanford, undaunted but surprised that she was one of only two openly gay students in her year. It was less easy, she says, on her parents, but they got used to it. After Stanford, she was the first out gay student to get a Rhodes scholarship to Oxford.

Aids activism

While still doing her doctorate there, on HIV/Aids and healthcare reform in British and American prisons, she moved to a squat near Arsenal football ground, got involved in Aids activism and had "an amazing social life – I'm actually surprised I managed to sustain it".

After three years, she returned to America and made money doing odd jobs, such as cleaning yards. One belonged to the artist Susan Mikula and Maddow fell in love. Over a decade later, they are still together; two of Mikula's photographs hang in her office and whenever Maddow refers to her partner, she smiles.

After winning the initial local radio gig she rose swiftly to working on a national station, Air America. She was soon making regular appearances on CNN and MSNBC before being given her own show in 2008, "and I'll stay until I start getting old, because you can't get old on TV, you know".

Maddow is one of the very few gay news anchors in America – well, one of the very few openly gay news anchors. Does she feel frustration towards an equally well-known news presenter who is widely assumed to be gay but has never come out? For the first time, Maddow pauses: "I'm sure other people in the business have considered reasons why they're doing what they're doing, but I do think that if you're gay you have a responsibility to come out," she says carefully.

In October 2009, I went to a talk Maddow gave as part of the New Yorker Festival and it is impossible to exaggerate the waves of adoration for her, particularly from the pairs of women who made up the majority of her capacity audience. While Maddow has a slightly uncomfortable relationship with her celebrity ("being recognised is not why I do this job"), the thought that she inspires pride in the gay community "gives me joy".

Just the way Maddow looks – "like a 13 year old boy" is her favoured self-description – is inspirational to all women, gay or straight. With her short brown hair and elegant if gangly body, she is a defiant rebuttal to the cookie cutter blonds who dominate US television. "I just don't think about how I look that much," she shrugs.

But she presumably hardly has time to anyway, with researching and writing her show every day and working on a book. I glibly express sympathy for her partner who must never get to see her.

"Oh," smiles Maddow, "I take up a surprising amount of space." On air and off.