Lesley Klaff taught law in the United States for seven years before taking up her post at Sheffield Hallam University in 1993. She was also Affiliate Professor of Law at Haifa University, 2007 - 12. Her research is in the field of contemporary anti-Semitism. She is the Associate Editor for the Journal for the Study of Antisemitism, an international, peer-reviewed journal and serves on the Academic Advisory Board of the Louis D. Brandeis Center for Human Rights under Law, a non-profit civil and human rights organisation in Washington DC established to combat anti-Semitism in higher education through research, education and advocacy.
Lesley also serves on the Advisory Board of the Berlin International Center for the Study of Antisemitism, a non-profit organisation dedicated to fighting anti-Semitism through research. She is a member of UK Lawyers for Israel (UKLFI), an NGO set up to provide pro-bono legal advice, assistance and representation to victims of anti-Semitism. Her responsibilities include giving advice to university students who experience anti-Semitic harassment on campus.
She appeared in the 2013 documentary on campus anti-Semitism, "Crossing the Line: The Intifada Comes to Campus," produced by Raphael Shore and directed by Wayne Copping, and was interviewed on footballer Niclas Anelka's use of the quenelle gesture for the Eurosport channel, broadcast on January 25th, 2014. Lesley appeared as a panel member at the Annual Liberal Democrat Conference in Glasgow, on September 16th, 2013, where she spoke alongside Alistair Carmichael MP, Maajid Naawaz of the Quilliam Foundation, and Mark Gardner of the Community Security Trust, on the topic of anti-Semitic discourse. She was also a witness for the claimant in Fraser v The University and College Union (March 22nd, 2013), which alleged institutional anti-Semitism against the UCU.