Sergey Dmitrievich Knyazev (; born 15 February 1959) is a Russian jurist and scholar of constitutional and administrative law who currently serves as the judge of the Constitutional Court of Russia since 2008.
Knyazev, born in 1959 in Pavlovsky Posad, Moscow Oblast, graduated with honors from the Law Faculty of Far Eastern State University in 1981, after which he completed postgraduate studies at the Law Faculty of Leningrad State University, defending his Candidate of Sciences (Ph.D. equivalent) thesis in 1985 on "Legal Support for Comprehensive Urban Development Planning (Administrative-Legal Aspects)".
Beginning his academic career in 1985 at Far Eastern State University, Knyazev progressed from assistant professor to Head of the Department of Constitutional and Administrative Law. From 1989 to 1990 he served as Deputy Dean of the Law Faculty, and from 1990 to 1995 as Dean while continuing to lead the department.
Knyazev played a key role in developing the Charter of Primorsky Krai, the fundamental law of the region adopted in 1995. From 1995 to 2008 he chaired the Electoral Commission of Primorsky Krai. In 1999, he defended his Doctor of Sciences (habilitation) thesis at Saint Petersburg State University on "Electoral Law in the Legal System of the Russian Federation (Theoretical and Practical Issues)".
In October 2008, following nomination by President Dmitry Medvedev and approval by the Federation Council, Knyazev was appointed judge of the Russian Constitutional Court. He concurrently serves as Professor of the Department of Administrative and Finance Law at the Saint Petersburg State University Faculty of Law.
In December 2022, amid Russia's invasion of Ukraine, Knyazev was added to the European Union sanctions list for "artificially creating the image of the legitimacy of Russia's invasion of Ukraine". He had previously been included in Ukraine's sanctions list.