From chick-lit to Cameron's A-list, her star never shone brighter than when she skewered the Murdochs. But now she says it's goodbye to Parliament and hello to the family. And America.

She blazed like an exotic firework across the skies of Westminster, before plummeting to the ground in what looked like an act of political suicide. Louise Mensch announced on Monday that two years after capturing Corby for the Conservatives, she has decided to stand down. Her loss is a blow to David Cameron, responsible for lighting Mensch's blue touchpaper, launching her on his unsuspecting party as one of his A-list of candidates.

When Cameron became leader, the Conservatives were shamefully short of women MPs. As Boris Johnson had put it a few years earlier: "The trouble with Tory associations is that they don't groove to chicks." Cameron tried to deal with this problem by assembling a list of candidates who had already had successful careers outside politics and about half of whom were women, and by coercing local Conservative associations into adopting these newcomers as candidates in winnable seats.

Louise Bagshawe, as she was then, had made her name as an author of chick lit; the Conservatives in Corby, an eminently winnable seat, were prevailed upon to groove to her. Such manoeuvres caused immense resentment among Tories who felt they had for many years borne the heat and burden of the day, only to see a collection of minor celebrities enter the Commons after doing virtually no political work at all.

John Hayes, chairman of the socially conservative Cornerstone Group of Tory MPs (motto: "Faith, flag and family"), denounced the A-list for containing "people who spend too much time with the pseuds and posers of London's chichi set and not enough time in normal Britain".

However, it would be unfair to describe Mensch as insubstantial. She is a devout Roman Catholic, who has said she is so afraid of flying that she prays to Padre Pio, St Bernadette, St Vincent de Paul, St Louise and John Paul II. Since 1995, she has also published, under her maiden name, the following novels: Career Girls, The Movie, Tall Poppies, Venus Envy, A Kept Woman, When She Was Bad…, and so the list goes on, reaching Desire (2010) and Destiny (2011).

Just reading the titles is enough to make some of us feel a bit tired. Mensch is first and foremost a successful professional writer and has shown impressive industry. What's more, her work has not remained completely unchanging over the years. As one anonymous but generally appreciative critic said of the main characters in A Kept Woman: "The chemistry between them simply sizzles, though Bagshawe, perhaps responding to a few criticisms of her earlier work, has reduced her sex scenes to three per book (rather than the 30 or so you get in her early work)."

If Mr Hayes is reading this, one can almost hear him snorting and saying that even such a dramatic reduction in the number of sex scenes in no way made Mensch suitable for the life of a Tory MP. But there is, oddly enough, a connection between her writing and her politics. For Mensch was inspired by Jeffrey Archer, a writer of bestsellers who was also for a time a highly influential figure in Tory politics.

In a 2001 interview with the Observer, Mensch said of Archer's work: "Kane and Abel is the best popular fiction of all time. As a kid, I wanted to be prime minister when I read First Among Equals. I love him. He's my hero."

It was quite brave, or at least eye-catching, of Mensch to say this, for Archer was at this point in prison. But at this stage, she was not, as far as we know, contemplating a career in politics. Instead, she declared, with the candour that can make her such a rewarding interviewee: "I want to retire very early, by the time I am 40, and go to live in Italy."

Mensch is now 41 and is going to live in New York rather than Italy, but by leaving the Commons she has fulfilled her dream of retiring at an unusually early age. In 2001, she confided that she was already "building up a portfolio of investments" because she wanted to be free to decide what she was going to do: "Money gives you the power to do whatever you want to do. I like the idea of being in complete control of my life."

This is a fantasy. Money does not give you the power to do whatever you want to do. But without being a fantasist, Mensch could not have written so many books. In order to write like Archer, you have to be able to fantasise like Archer. You have to believe this stuff while you are writing it or you will never get beyond page three.

Perhaps the simple truth about Mensch is that she is entirely sincere and has the capacity to believe in something while she is doing it. Her latest venture, which will presumably now receive more of her attention, is the social media site, named Menshn (just in case you might forget who runs it).

In 1998, she announced that she was going to New York in search of a husband. Lo and behold, she managed to find one: an Italian-American property developer called Anthony LoCicero. They married in 2002 and had three children. But the couple separated in 2009 and she subsequently married Peter Mensch, a celebrated New York music industry figure she had known since she was a student at Oxford, who had helped her to find work in the music industry, and to whom she had dedicated her first novel.

In 2006, she yielded to another fantasy to which no doubt she was sincerely attached at the time. She decided to become a Conservative MP, after which it could be expected that she would very soon rise to dizzying levels of power and influence. Thanks to Cameron's support, she became the candidate for Corby, an oddly mixed constituency, for as well as Corby – a former steel town which had drawn in thousands of Labour-voting Scottish immigrants – it includes a large tract of Tory-voting rural Northamptonshire. Mensch said the property there reminded her of the Cotswolds, but with the great advantage of being cheaper: "I'm pleasantly surprised at what I can get for my money up here. It's fantastic."

After her election in 2010, Mensch rapidly began to make a name for herself at Westminster. One admiring Tory described her to me as "brave and brainy". She brought a touch of glamour to a party that is still not rich in that quality and displayed a gift not just for publicity, but for asking incisive questions. When the culture, media and sport select committee interrogated Rupert and James Murdoch, Mensch helped to prevent the scene being dominated by Tom Watson, the Labour MP who had made much of the running in the attack on News International.

Mensch also responded well when she was asked whether she had taken drugs while working, in her youth, in the music industry.

She said this was "highly probable", and later added: "I did serious drugs and it messed with my head. It's had long-term mental health effects on me. It's something that I regret incredibly." But Mensch also started to wonder if she was ever going to get promoted, asking in an interview (with GQ) in February: "It's kind of annoying. What do I have to do to get promoted? Am I being disloyal?"

The answer to that question is now yes. By jumping ship, it could be argued she has let down everyone from Cameron to her local party. Corby will almost certainly go Labour again, which it might well have done at the general election expected in 2015, for Mensch does not appear to have taken as much trouble as she might have done to entrench herself in its people's affections. But for many, especially Tories, the decent thing would have been to wait until then to step down.

By her own lights, Mensch has been honest. In words that could have come from one of her novels, she wrote: "Dear Prime Minister, As you know, I have been struggling for some time to find the best outcome for my family life, and have decided, in order to keep us together, to move to New York…"

No wonder a touch of asperity could be detected in Cameron's reply: "It goes without saying that I had wished to see you serve for longer and at a more senior level."

The prime minister had done all he could for her, only to find himself written out of the script. Mensch has already started a new story in which she sets sail from Westminster to conquer the New World.