Robert S. Lasnik (born 1951) is a United States federal judge, on the U.S. District Court for the Western District of Washington.
Born in Staten Island, New York, Lasnik received an A.B. from Brandeis University in 1972 and an M.S. in journalism from Northwestern University in 1973, an M.A. in education also from Northwestern University in 1974, and a J.D. from the University of Washington School of Law in 1978. He was a deputy prosecutor in the King County Prosecuting Attorney's office from 1978 to 1981, a senior deputy prosecutor from 1981 to 1983, and a chief of staff in that office from 1983 to 1990. He served as a superior court judge on the King County Superior Court from 1990 to 1998.
Lasnik was nominated to the U.S. District Court for the Western District of Washington by President Bill Clinton on May 11, 1998, to a seat vacated by Carolyn R. Dimmick. He was confirmed by the United States Senate on October 21, 1998, and received his commission on October 22, 1998. He served as chief judge from 2004 to 2011.