Ryan had one year left on his current three-year deal.
Dallas, which was eliminated from playoff contention during the final week of the regular season, finished 19th in the NFL in total defense this year.
Cowboys owner/general manager Jerry Jones had hinted in previous weeks "changes" would be coming.
Thus far, this is the first ax to drop.
More to come on this breaking story.
Rob Ryan fired
Breaking Burgundy Top Stories
Quick Move: Redskins Add Veteran ReceiverFormer Rams second-round pick Brian Quick is the newest receiver for the Redskins.
Breaking BurgundyFriday at 7:35 AM
The Potential Flaw In Manusky's PlanThe Redskins need a nose tackle. It sounds like that might come via the NFL Draft. Ben Standig on why that's a risky plan.
Redskins Depth Chart: Now What?Terrelle Pryor and D.J. Swearinger are in, Ricky Jean Francois and Pierre Garcon are out. More moves on deck.
McShay Talks Redskins, 2017 QuarterbacksThe Kirk Cousins topic became a tangential question for the ESPN NFL Draft analyst, who also revealed his latest mock draft.
Redskins And Cousins Living In The Spin RoomThe latest Kirk Cousins interview reshaped the contract talk with the Redskins. Ha, as if. Neither side is showing their hand publicly. Both have moves to make.