[2] Rob played defensive end opposite his brother, Rex, at Southwestern Oklahoma State University.

He then spent five seasons at Tennessee State, where he coached running backs (1989–91), wide receivers (1992) and the defensive line (1993).

With Ryan as his position coach, cornerback Aeneas Williams earned two trips to the Pro Bowl in 1994 and 1995.

After being fired by the Arizona Cardinals, Ryan served as defensive coordinator at Hutchinson Community College in 1996.

While at Oklahoma State, the Cowboys defense continually ranked among the best in the nation, also he was named Coordinator of the Year by The Sporting News in 1997.

It was an over 100-yard improvement per game from the year before and helped the Cowboys produce an 8–4 mark and capping the 1997 season with a berth in the Alamo Bowl.

Ryan's unit also contributed to one of the best scoring defenses in franchise history in 2001, as the Patriots allowed just 17 points-per-game and produced Pro Bowlers Willie McGinest and Tedy Bruschi.

[14] In January 2013, Ryan agreed to become the defensive coordinator for the St. Louis Rams, but resigned less than five days later.

On November 16, 2015, the day after a 47–14 loss to the Washington Redskins, and with New Orleans' defense ranked last in the NFL, Ryan was fired.

[22] On January 5, 2020, the team announced that incoming head coach Ron Rivera had replaced Ryan with Steve Russ.

On January 21, 2025, Ryan was hired by USC as the team's assistant head coach for defense/linebackers for the 2025 season.

[30] In September 2017, Ryan was hired by Fox Sports to host a radio show with Mark Willard.

In 2018, Ryan became a weekly analyst of Sky Sports' NFL coverage in the UK and Ireland.

[31] In 2012, following in the footsteps of his brother, Ryan had lap band surgery in an attempt to lose weight.