Marshall had appealed the original NFL suspension and learned Thursday of the reduction.
He also forfeits his pay for an additional game, for a two-game total of $52,352.
NFL Commissioner Roger Goodell suspended Marshall for violating the NFL personal conduct policy with a series of misdeeds. At the time, Marshall was told the suspension could be cut to two games if he stayed out of trouble and kept in touch with a league-appointed counselor.
Goodell reduced the penalty after Marshall went to New York last week to appeal.
Marshall's suspension begins Saturday. He can return to Broncos headquarters Sept. 9.
Marshall caught 102 passes for 1,325 yards and 7 touchdowns last season and has shown no falloff this summer despite suffering a gash on his right arm that required emergency surgery this spring and sidelined him for almost all of the team's offseason field work.
Copyright 2008 by The Associated Press