Brenda Hoggett, QC, the law commissioner and academic, starts her duties sitting in the Family Court as Mrs Justice Hale.
Professor Hoggett, aged 48, who was behind the Government's no-fault divorce reforms announced last month, is the first academic to be appointed to the bench.
She was a university lecturer before joining the Law Commission, the body which advises the Government on reforming the law, nine years ago.
She will replace Mrs Justice Booth, who is retiring, and will be sworn in on 12 January.
Legal and law reform groups have complained that the High Court judiciary is drawn from too narrow a base. Until this year, when the
first solicitor was appointed to the bench, all High Court judges had been practising barristers.
Her appointment has been welcomed by legal academics, barristers and lawyers. Professor Hoggett, who as Mrs Justice Hale will be known by her maiden name, is an expert on family law.
At the Law Commission, she spearheaded changes which led to the 1989 Children Act and last month's proposals for divorce on demand with a one- year waiting period.
A keen advocate of using mediation in divorce cases, a key part of the proposals, she is chairwoman of National Family Mediation, the umbrella group for mediation services.
She has sat as a part-time judge since 1989 and wrote in the group's recent annual report that the more cases she decided in the traditional way, the more she realised that 'a properly and freely agreed solution' was better than one imposed by a court.
Educated at Girton College, Cambridge, she joined Manchester University's law faculty in 1966 and was appointed a professor in 1986. Since 1990 she has been a visiting professor at King's College, London.
Professor Hoggett was formerly married to a Manchester barrister, by whom she has a daughter aged 20. She was married again a year ago, to Julian Farrand, the insurance ombudsman and a former law commissioner.
In her Who's Who entry she lists her recreations as 'domesticity and drama'.
Victor Moore, Professor of Law at the University of Reading, said: 'I think it's a very good appointment. I look forward to her making quite a contribution to family law development.
'She's got great experience in the academic world and also as a law commissioner. It also strengthens the female base of the judiciary, which is sadly needed.'
Gareth Williams, former chairman of the Bar Council, said: 'I personally think it is a very good idea for two reasons. One, it's good to have a better representation of women on the High Court bench, although it's still lamentably insufficient.
'More important, I think, is that I have always personally favoured bringing in people who have not necessarily spent all of their lives in practice and can have something else to offer, and of course she's really coming from more of an academic, law commissioner background than someone who has been in full-time practice. Its a very good step forward.'
Mr Williams added that in making the appointment the Lord Chancellor had displayed 'a useful flexibility'.
'Its an extrememely interesting advance. Its not unknown in America, where there's much more transference of academic lawyers, going into practice and back again and then on to the bench.'
In this case, he added, it was not as if a non-practising lawyer had been asked to preside over criminal or complex fraud cases which required specialist skills and experience.
Another legal observer said: 'She will be a brilliant judge. She's got wide-ranging knowledge. Her work on divorce law reform showed that she's perfectly in touch with the theory and practice of law and how it affects people's lives.'
Whether Professor Hoggett's appointment to the bench will be the first of many such 'lay' appointments remains to be seen.
A spokesman for the Lord Chancellor's Department said last week that 'people are chosen according to their suitability for the posts in question'.
Only time will tell whether the Lord Chancellor, Lord Mackay of Clashfern, will make equally imaginative appointments in future.