Internationally, Ruff was an assistant coach for the Canadian national team at the 2010 and 2014 Winter Olympics, winning gold medals at both.

An illustration of this came in a May 10, 1980, playoff game against the New York Islanders, when opposing goaltender Billy Smith struck Ruff with his stick as he passed in front of his net.

His greatest success as an assistant coach was with the 1995–96 Florida Panthers, who made it to the Stanley Cup Finals before losing to the Colorado Avalanche in a four-game sweep.

In Ruff's second season as coach, the Sabres reached the 1999 Stanley Cup Finals before losing to the Dallas Stars in six games.

Buffalo missed the playoffs in the three seasons preceding the 2004–05 NHL lockout amidst the team's bankruptcy and financial problems caused by the Adelphia Communications corporate scandal.

After the lockout, Ruff led the Sabres to back-to-back Eastern Conference Finals appearances only to lose to the Carolina Hurricanes in 2006 and the Ottawa Senators in 2007.

Ruff was the longest-tenured coach in the NHL and was rewarded with a three-year contract extension that had an option for a fourth season.

In his post-game interview following a questionable hit on Jochen Hecht, that knocked the Sabres centre out of the lineup for two weeks with a sprained ACL in the 2005–06 season, Ruff said, "I want him [Tucker] suspended."

[8] Because the hit to Drury did not result in a penalty, Ruff sent out Andrew Peters, Patrick Kaleta and Adam Mair, the team's "enforcers".

The goaltenders also entered the fight, with Martin Biron challenging Ray Emery, and Ruff himself engaged in a prolonged shouting match with Senators head coach Bryan Murray.

[9] A large contingent of Sabres fans attempted to raise money to pay the fine on Ruff's behalf.

Ruff was named as an associate coach for Canada, which won the gold medal at the 2010 Winter Olympics in Vancouver.

Al Arbour won more games for the New York Islanders, but he also coached the St. Louis Blues early in his career.

[19] In 2014, Ruff led the Stars to their first playoff appearance since 2008, but lost in the opening round to the Anaheim Ducks in six games.

The 2021–22 season had begun with some hopes based on offseason acquisitions and the maturation of young star players, but the team was plagued by injuries, using a franchise record seven different goaltenders over its 82 games.

However, the team's fortunes changed rapidly, and by the end of October, they were embarking on a lengthy winning streak that would carry them into first place in the Metropolitan Division.

[32] On May 17, 2023, Devils general manager Tom Fitzgerald announced that Ruff would be retained as team's head coach after his contract expired at the end the 2022–23 season.

Another younger brother, Marty Ruff, was a first-round draft pick of the St. Louis Blues but never appeared in an NHL game.