Roethlisberger, who won Super Bowls with the Steelers in 2006 and 2009, was accused in March of sexually assaulting a 20-year-old female college student in a Georgia nightclub.
The 28-year-old quarterback was not charged with any crime but NFL commissioner Roger Goodell had said Roethlisberger had still violated the league's personal conduct policy.
"The commissioner's decision to suspend me speaks clearly that more is expected of me," Roethlisberger said in a statement posted on the Steelers website (www.steelers.com). "I am accountable for the consequences of my actions.
"Though I have committed no crime, I regret that I have fallen short of the values instilled in me by my family.
"I will not appeal the suspension and will comply with what is asked of me -- and more."
As part of his suspension Roethlisberger must undergo behavioral evaluation and cannot participate in any off-season team activities until he is assessed by medical professionals.
Goodell said he will review Roethlisberger's progress prior to the start of the regular season and could reduce the suspension to four games.
The commissioner added, however, that he could extend the suspension if Roethlisberger fails to co-operate with its terms.
"Missing games will be devastating for me," said Roethlisberger. "I am sorry to let down my team mates and the entire Steelers fan base.
"I am disappointed that I have reached this point and will not put myself in this situation again.
"I appreciate the opportunities that I have been given in my life and will make the necessary improvements."
(Writing by Steve Keating in Toronto; editing by Steve Ginsburg)