Joyce has a law degree from Bristol University, the Diploma in Social and Administrative Studies (distinction) from the University of Oxford and the Certificate of Qualification in Social Work. After a short period as a probation officer in Oxfordshire and a social worker in her home city of Glasgow, she went to the United States where she worked as a probation officer in Chicago before taking the Bar exam. She is admitted to both the Court for the Northern District of Illinois and the U.S. Supreme Court. Her career then took her to Washington D.C. as Attorney Advisor in the Administrative Office of the US Courts. In 1981 she was awarded a Judicial Fellowship by the Supreme Court of the United States and the Justice Tom C. Clark award. On completion of the Fellowship, she joined the Federal Judicial Center as Senior Systems Analyst where she served until her return to Britain in 1983. She worked for the Home Office evaluating magistrates’ courts computer systems, then spent time as a Research Fellow at the Centre for Criminological Research, University of Oxford and the Institute of Judicial Administration, University of Birmingham. Joyce also worked as a children’s guardian for 10 years and chaired the Lord Advocate’s steering group on visual recording of joint investigative interviews of children from 2004 to 2005. Joyce is a member of the pool of experts advising the Diversity and Development Committee of the Judicial College. Joyce has been given the 2013 Administration of Justice award by the US Supreme Court Fellows Association.

In 1991, Joyce formed a Partnership with Richard Woolfson to undertake research and consultancy assignments on behalf of government departments involved in the operation of the legal system. The Partnership later incorporated to become Lexicon Limited.

In the 2015 New Years Honours List, Joyce was made a Dame Commander of the Order of the British Empire for services to justice, particularly vulnerable and child witnesses.

In September 2016, Joyce was awarded an honorary Doctor of Laws by the University of Hertfordshire.