Born in 1951, Mark Sidran grew up in Seattle's Seward Park neighborhood, attending Franklin High School and serving as president of his senior class. After earning a BA in government at Harvard, he received his law degree from the University of Washington in 1976. He worked for the King County Prosecutor's Office from 1975 to 1985, and was a partner in the law firm of McKay & Gaitain from 1986 to 1989. In 1990, he became Seattle's City Attorney, holding that office through 2001.

During Sidran's tenure, one of his signature issues was the impoundment of cars of people caught driving with suspended licenses. He endorsed the law as promoting responsibility and increasing public safety, while his critics claimed the practice disproportionately affected the poor. Sidran's advocacy of "civility laws" - ordinances outlawing aggressive panhandling and sitting on sidewalks - caused a great deal of controversy, as did his crackdowns on problem nightclubs.

In 2001, Sidran chose to run for mayor instead of seeking a fourth term as city attorney. After losing the mayoral race to Greg Nickels, Sidran practiced with McKay Chadwell and served as chair of the Washington State Utilities and Transportation Commission. He ran unsuccessfully for Washington State Attorney General in 2004.