Mr Justice Munby has been appointed chairman of the Law Commission, for three years from 1 August, the Lord Chancellor has announced.
Sir James succeeds the Right Honourable Lord Justice Etherton, who has completed his term of office as Chairman.
The new Chairman said: "I am delighted to have been appointed Chairman of the Law Commission. The Commission has made, and continues to make, a significant contribution to the law. I am very much looking forward to ensuring that the importance of this contribution is maintained and continues to be recognised."
The Law Commission was set up in 1965 to keep the law of England and Wales under review, and to recommend reform where it is needed.
Sir James was called to the bar in 1971, was appointed Queen's Counsel in 1988 and then appointed as a High Court Judge in 2000, assigned to the Family Division and the Administrative Court. He has been a leading proponent of opening up the family courts.
The Lord Chancellor, Jack Straw, said: "I am confident that Sir James Munby, with his skills and experience, will be of great value to the Law Commission and will further enhance the important work they carry out. I look forward to his contribution over the next three years."