Sean Christopher Marshall (born August 30, 1982 in Richmond, Virginia) is a Major League Baseball left-handed pitcher for the Chicago Cubs. After three minor league seasons, Marshall was added to the Cubs' 40-man roster in November 2005.

Marshall graduated from Manchester High School in Midlothian, Virginia, in 2000. He attended Virginia Commonwealth University, and was drafted by the Cubs in the sixth round of the 2003 Major League Baseball Draft. Marshall spent three years in the minor leagues before being promoted to play with the Cubs, and had 24 starts in his rookie season in 2006. Marshall started the 2007 season on the disabled list, but returned to the Cubs' rotation in mid-May.

Marshall's twin brother Brian also plays baseball, and was taken in the fifth round of the same draft by the Boston Red Sox.