Rosemary Canter: Publisher who became a leading literary agent specialising in children's books

Poised, chic and unflappable, Rosemary Canter was the image of the literary agent, coolly supportive of her creative charges, robust in negotiation with publishers, financially savvy and seldom wrong in her judgements. As a leading literary agent with United Agents, her clients included William Nicholson, Ian Whybrow, Giles Andreae, Ros Asquith, Korky Paul and Sophie McKenzie.

She was born in Golders Green, north London, in 1949 to Philip and Eileen Canter. Her father was a solicitor who worked until his mid-eighties. At the direct-grant South Hampstead High School for girls, she was precociously sophisticated and worldly wise. She's remembered by contemporaries for directing a production of one of Christopher Fry's precious verse-dramas with steely resolve and crisp notes. Signs of her later perfectionism were already apparent, as well as her passion for literature and ideas. At Newnham College, Cambridge, she gained a 2:1 in history and wrote for Varsity.

Her career fell into two halves: 17 years as a publisher, 20 years as an agent. Always a voracious reader, she struck gold in 1972 with her first job, as assistant fiction editor at Penguin Books. There she joined a glamorous cabal of young Turks – Peter Carson, Caradoc King, Geraldine Cook, James Cochrane, Paul Sidey, Marianne Velmans, Brenda Gardner – all of whom would become hotshots in London's publishing houses and literary agencies. They stayed friends, rendezvousing every Christmas, usually at Rosemary's east London home.

The atmosphere at Penguin Books' editorial office in John Street in the early 1970s still carried a whiff of the Woodstock generation. The work ethic was laid-back to a startling degree. Marijuana plants were rumoured to flourish on the fire escape. No one confessed to a driving ambition or passion to get on, to make a million, to shift units: their interest was to read the best modern writing available and see if it was right for Penguin – and to swan about at parties. Rosemary later said that, just out of university, she thought such behaviour was standard in the world of books; reality rudely intruded when Penguin made her redundant in 1975.

It was an uncertain time in publishing. She joined and left the Elsevier Press, Macmillan, Hutchinson and Methuen over the next decade. But each redundancy payment went towards buying a house and, amidthe comings and goings, she discovered her métier. At Macmillan, she was given responsibility for an encyclopaedia (entitled Look It Up) aimed at six-year-olds and, from this unpromising start, developed a sure feel for children's books. She commissioned works of fiction, illustrated books, books of adventures and games, novelty books, activity books for bored pre-pubescents. Her proudest moment, in these early years was discovering the work of Brian Jacques, whose 22 Redwall novels for children eventually sold 20m copies worldwide, on the unsolicited slush pile at Beaver Books.

Children's book publishing was still a cottage industry, yet to be transformed into a serious concern. Rosemary studied the market empirically: she helped set up the Children's Book Circle discussion group – characteristically, she worried that the word "Circle" was too evocative of Sewing – for publishers to share expertise. She visited comprehensive schools to ask what the scholars were reading and what they'd like to read. She worked for a year as children's book editor at the Sunday Times, explaining to mystified colleagues the distinction between the seven-11 age group and the eight-12 age group (it's about the interface between reading ability and maturity of understanding). And at a time when teenage, or Young Adult, fiction was taking off in the US but no publisher seemed able to crack it in the UK, Rosemary made a successful foray into the 13-plus market, launching a teen paperback list at Methuen in 1987.

Two years later, she was asked to develop a children's list at the Peters, Fraser and Dunlop literary agency. It was a new challenge, with pressure to get the best deals for her clients while being their nanny, agony aunt and No 1 fan. Over the next 20 years, she put her natural confidence and straight-talking in the service of an impressive roster of writers. She soon had 50 clients under her direct supervision.

She was always keen to extend the boundaries of the job, organising a conference in 1993 to introduce children's publishers to the world of interactive publishing. In 1997, she accepted an invitation by the Cheltenham Literary Festival to programme its children's events, a new role into which she threw herself with energy.

In 2008, she was one of a group of PFD agents who, faced with a takeover, decided to break away and form their own agency, United Agents. All her clients came with her. They loved her as a friend as well as a negotiator, and she was maternally proud of their achievements. But she never stopped looking for the next project, the new talent.

A restless traveller, she courted adventure far from London's publishing milieu. She travelled to Libya with a friend and wound up in the desert, 1,000 miles south of Tripoli, camping in a bender tent. Though supper was camel stew, and there was no water for washing, she would emerge into the pre-dawn light with an elegant Tuareg turban draped around her head, and eat a hearty breakfast. Selling a pre-first-edition proof copy of Harry Potter and the Philosopher's Stone, online, to a buyer in Beverly Hills for $3,000 enabled her to visit Australia. In Japan, she climbed a volcano and loved bathing in the communal, open-air hot baths. She explored shops in Tokyo and Kyoto where hand-made paper was sold, and would spend an hour pulling out sheet after sheet, looking for the perfect hybrid of texture and translucency.

As her illness took hold, she became more and more attached to colours. She was an accomplished knitter, and heaps and balls of vividly dyed wools would lie around her living-room. She bought rugs and stools in pink and orange shades, and returned from trips to Columbia Road flower market festooned with armfuls of blooms.

Her home in Mile End became, at the end, a kind of shrine to colourand warmth. She spent her last weeks holding court, with her cat Cinnamon, to scores of visitors, so many thatshe needed secretarial help to deal with them all. She never married.She is survived by her youngerbrother, the novelist and scriptwriter Jon Canter, and a large army of clients and friends.

Rosemary Canter, publisher and literary agent: born London 11 April 1949; died London 11 March 2011.