Usually when giving an acceptance speech for an award it is unwise to attack the saintly figure of Helen Mirren, who is every bit as beloved in America as she is in Britain. But then Tina Fey has been breaking rules for some time in search of a good joke. So last week in New York, as Fey accepted a Comedy Awards gong for her role in the not especially memorable film Date Night, she launched into an apparently po-faced assault.

"The only thing I knew for sure when we were making this movie was that I was fucking crushing Helen Mirren at acting," she said, clutching her award. "If you watch Date Night next to The Queen it is embarrassing for her." As the audience collapsed into giggles, she added mournfully: "But, you know what, she looks great in a bathing suit."

It was vintage Fey, combining sharp satirical wit with a faux seriousness and a sudden attack of insecurity. It was the sort of thing that her most famous alter ego, Liz Lemon from the hit TV sitcom 30 Rock, could easily have said herself. No wonder the clip went viral.

Yet, in order to work, the joke relied on disingenuousness: the idea that Fey stands in the shadow of someone like Mirren. The truth is that might not be the case, for she has rapidly spread across America's cultural landscape, from late-night comedy to primetime television to movies.

Nor is her realm limited to television and Hollywood. Fey has graced numerous magazine covers and this week sees the release of her autobiography, Bossypants. Two excerpts have appeared in the New Yorker: an honour more often associated with renowned writers.

By any standards it is a remarkable rise – but it is made more so because Fey is rocketing skywards as a successful woman in the overwhelmingly male-dominated world of comedy. She is also doing it by dint of an intelligent, witty brand of humour that slyly undercuts the usual celebrity obsession with looks. Women across the US are taking notice and anointing Fey in perhaps her least expected role so far: that of feminist pioneer.

"Tina is a huge breakthrough," said Judy Carter, a standup comic and motivational speaker. "She is a trailblazer. She has climbed every mountain and succeeded, and she is a huge role model for women."

Fey's high profile to a large extent lies with the success of Liz Lemon, the main character in 30 Rock, who is the lead writer of a late-night comedy show. Fey plays Lemon as a dishevelled geek who frets about not having any sex. She eschews any interest in fashion or dressing sexily and relies on her brain and wits to get through each episode, though not always successfully. Fey plays the character with warmth and a clumsy vulnerability which only adds to the comedy.

"Liz Lemon is so self-deprecating but she also keeps zinging out these witty humour barbs underneath that," Carter said. Lemon's insecurities, combined with her independent career girl persona, make her a role model for many modern women.

It is hard to get away from the fact that Lemon and Fey are intimately bound up with each other. After all, Fey was lead writer on Saturday Night Live from 1999 to 2006 and is a successful woman in a man's world of comedy television. 30 Rock bears more than a passing resemblance to Saturday Night Live. Indeed many of the passages extracted from Bossypants could easily be made into episodes of 30 Rock (and perhaps many have been). They often address the problems of being a woman in the comic world, usually in funny and surreal ways.

"The men urinate in cups. And sometimes jars," she observes of her fellow writers in one chapter, before detailing the habit in hilarious prose. "Not all of the men at SNL whizzed in cups. But four or five out of 20 did, so the men have to own that one. Anytime there's a bad female standup somewhere, some idiot interblogger will deduce that 'women aren't funny'. Using that same math, I can deduce that male comedy writers also piss in cups," she said.

Clearly Fey is not afraid to give as good as she gets in her working environment, which perhaps explains why she has done so well. Unlike some successful female comedians, such as Sarah Silverman, Fey has not had to outswear and outoffend her male rivals to do well. Instead she sticks to her strengths, trusting that her sly intelligence will carry her through.

"TV really has been a pretty male-dominated field. To get where she is, Tina Fey has had to break through a lot of walls," said Adam Frucci, who runs the comedy blog Splitsider. On her way she has also been unafraid to punch out at not just men but more traditional depictions of women.

One of the most ground-breaking and devastating moments in recent US comedic history was Fey's Saturday Night Live impression of former Alaskan governor Sarah Palin during the 2008 election campaign. Fey skewered Palin's mom-turned-mama-grizzly political persona with such accuracy that it became a pop culture sensation.

But at the same time she was also skewering the representation of women that many thought Palin symbolised: the conservative, "hockey mom" values and ignorance of a wider world. It reached its apogee in a Saturday Night Live skit with Amy Poehler playing Hillary Clinton as the pair issued a joint statement condemning sexism in politics. The two stood together at a plinth and addressed America. "I believe diplomacy should be the cornerstone of any foreign policy," Clinton intoned seriously, before Palin chirped: "I can see Russia from my house!"

As the sketch went on, Fey perfectly captured a preening, posing, ignorant Palin against Poehler's stunned and amazed Clinton, who by that time had lost the Democratic presidential nomination to Barack Obama. "Can you believe it, Hillary?" Fey's Palin asked as she described how she was now closer than Clinton to getting into the White House. Poehler's barely-in-control Clinton yelled back: "I cannot!"

But no one becomes a role model – and certainly not a feminist one – without also experiencing a backlash. Whereas Fey has exposed as baloney the old sexist myth that women are not as funny as men, some critics question her role as a women's rights heroine. They point out that while she is not a classic, busty, model-like example of beauty, on magazine covers she has not been shy of exposing a lot of skin. In a 2009 photoshoot for the style bible Vanity Fair she posed in underwear, with plenty of cleavage showing, just like a legion of Hollywood starlets before her.

"If Tina Fey were ugly then she would not have the career that she has had," said Jill Filipovic, founder of the blog Feministe. "We still don't see a lot of unconventionally attractive women on TV."

Others also point out that Liz Lemon's character can easily be interpreted as conforming to a traditional female stereotype: that of the lonely, insecure female, desperate for a man in her life. Put in that way, Fey, in the guise of Lemon, is hardly tearing down the walls of a sexist medium.

Some critics have also pointed to skits and jokes in which Fey has attacked other women. In a series of Saturday Night Live jokes about famous men having affairs, Fey lambasted the "other women" rather than mocking the men – a classically sexist case of blaming a "scarlet woman" for a husband's affair. She even called them "whores".

But maybe that says more about the boundaries and conventions of modern culture than it does about Fey and her political beliefs or cause. After all, she is not a social revolutionary but a comic trying to be funny. She also happens to be a woman and thus has to shoulder the burdens of her gender as she blazes a path.

"She is in a tough position," said Frucci. "Not many comedians are forced to represent their entire gender when all they are just trying to be is funny."

Tina Fey is a funny woman in a man's world and it is a testament to her success that even her critics are often also her fans. "Overall she is a positive force," said Filipovic, whose blog has at times carried anti-Fey analysis pieces. "I am a huge Tina Fey fan. I think she is hilarious."